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 $184.60   9.372%   $201.9007   $201.90   $201.90   $201.90  
  Purchase #2 $58.91   10.248%   $64.9471   $64.95   $64.95   $64.90  
  Purchase #3 $189.93   12.181%   $213.0654   $213.07   $213.05   $213.10  
  Purchase #4 $133.92   12.426%   $150.5609   $150.56   $150.55   $150.60  
  Purchase #5 $163.80   13.183%   $185.3938   $185.39   $185.40   $185.40  
  Purchase #6 $203.38   6.404%   $216.4045   $216.40   $216.40   $216.40  
  Purchase #7 $61.73   12.584%   $69.4981   $69.50   $69.50   $69.50  
  7 purchase totals = $996.27       $1,101.7705   $1,101.77   $1,101.75   $1,101.80