Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $189.62   8.212%   $205.1916   $205.19   $205.20   $205.20  
  Purchase #2 $152.96   13.333%   $173.3542   $173.35   $173.35   $173.40  
  Purchase #3 $134.26   10.730%   $148.6661   $148.67   $148.65   $148.70  
  Purchase #4 $216.29   13.285%   $245.0241   $245.02   $245.00   $245.00  
  Purchase #5 $217.76   4.844%   $228.3083   $228.31   $228.30   $228.30  
  Purchase #6 $134.98   11.601%   $150.639   $150.64   $150.65   $150.60  
  Purchase #7 $161.36   11.334%   $179.6485   $179.65   $179.65   $179.60  
  7 purchase totals = $1,207.23       $1,330.8318   $1,330.83   $1,330.80   $1,330.80