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 $156.32   12.756%   $176.2602   $176.26   $176.25   $176.30  
  Purchase #2 $227.97   9.729%   $250.1492   $250.15   $250.15   $250.10  
  Purchase #3 $199.42   8.766%   $216.9012   $216.90   $216.90   $216.90  
  Purchase #4 $250.60   6.846%   $267.7561   $267.76   $267.75   $267.80  
  Purchase #5 $210.42   10.124%   $231.7229   $231.72   $231.70   $231.70  
  Purchase #6 $96.74   10.850%   $107.2363   $107.24   $107.25   $107.20  
  Purchase #7 $53.90   5.437%   $56.8305   $56.83   $56.85   $56.80  
  7 purchase totals = $1,195.37       $1,306.8564   $1,306.86   $1,306.85   $1,306.80