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 $119.42   10.721%   $132.223   $132.22   $132.20   $132.20  
  Purchase #2 $102.70   8.719%   $111.6544   $111.65   $111.65   $111.70  
  Purchase #3 $162.34   5.605%   $171.4392   $171.44   $171.45   $171.40  
  Purchase #4 $229.48   3.337%   $237.1377   $237.14   $237.15   $237.10  
  Purchase #5 $62.72   6.578%   $66.8457   $66.85   $66.85   $66.80  
  Purchase #6 $154.41   10.365%   $170.4146   $170.41   $170.40   $170.40  
  Purchase #7 $224.31   9.719%   $246.1107   $246.11   $246.10   $246.10  
  7 purchase totals = $1,055.38       $1,135.8253   $1,135.82   $1,135.80   $1,135.70