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 $116.45   13.527%   $132.2022   $132.20   $132.20   $132.20  
  Purchase #2 $208.75   4.715%   $218.5926   $218.59   $218.60   $218.60  
  Purchase #3 $215.86   11.791%   $241.3121   $241.31   $241.30   $241.30  
  Purchase #4 $14.77   11.514%   $16.4706   $16.47   $16.45   $16.50  
  Purchase #5 $167.76   5.672%   $177.2753   $177.28   $177.30   $177.30  
  Purchase #6 $100.60   11.829%   $112.5   $112.50   $112.50   $112.50  
  Purchase #7 $72.92   5.629%   $77.0247   $77.02   $77.00   $77.00  
  7 purchase totals = $897.11       $975.3775   $975.37   $975.35   $975.40