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 $245.83   5.764%   $259.9996   $260.00   $260.00   $260.00  
  Purchase #2 $148.32   12.504%   $166.8659   $166.87   $166.85   $166.90  
  Purchase #3 $70.32   5.810%   $74.4056   $74.41   $74.40   $74.40  
  Purchase #4 $176.54   10.322%   $194.7625   $194.76   $194.75   $194.80  
  Purchase #5 $237.29   7.639%   $255.4166   $255.42   $255.40   $255.40  
  Purchase #6 $5.85   5.189%   $6.1536   $6.15   $6.15   $6.20  
  Purchase #7 $140.36   3.479%   $145.2431   $145.24   $145.25   $145.20  
  7 purchase totals = $1,024.51       $1,102.8469   $1,102.85   $1,102.80   $1,102.90