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 $210.28   10.638%   $232.6496   $232.65   $232.65   $232.60  
  Purchase #2 $209.39   9.668%   $229.6338   $229.63   $229.65   $229.60  
  Purchase #3 $40.70   11.796%   $45.501   $45.50   $45.50   $45.50  
  Purchase #4 $93.71   13.763%   $106.6073   $106.61   $106.60   $106.60  
  Purchase #5 $131.33   13.136%   $148.5815   $148.58   $148.60   $148.60  
  Purchase #6 $46.64   5.433%   $49.174   $49.17   $49.15   $49.20  
  Purchase #7 $250.59   6.402%   $266.6328   $266.63   $266.65   $266.60  
  7 purchase totals = $982.64       $1,078.7800   $1,078.77   $1,078.80   $1,078.70