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 $156.41   12.709%   $176.2881   $176.29   $176.30   $176.30  
  Purchase #2 $23.68   3.182%   $24.4335   $24.43   $24.45   $24.40  
  Purchase #3 $175.59   6.303%   $186.6574   $186.66   $186.65   $186.70  
  Purchase #4 $166.26   5.575%   $175.529   $175.53   $175.55   $175.50  
  Purchase #5 $245.90   3.184%   $253.7295   $253.73   $253.75   $253.70  
  Purchase #6 $23.59   7.812%   $25.4329   $25.43   $25.45   $25.40  
  Purchase #7 $67.71   5.403%   $71.3684   $71.37   $71.35   $71.40  
  7 purchase totals = $859.14       $913.4388   $913.44   $913.50   $913.40