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 $47.56   6.409%   $50.6081   $50.61   $50.60   $50.60  
  Purchase #2 $100.95   3.756%   $104.7417   $104.74   $104.75   $104.70  
  Purchase #3 $110.87   13.691%   $126.0492   $126.05   $126.05   $126.00  
  Purchase #4 $23.92   13.320%   $27.1061   $27.11   $27.10   $27.10  
  Purchase #5 $147.52   5.404%   $155.492   $155.49   $155.50   $155.50  
  Purchase #6 $46.74   8.727%   $50.819   $50.82   $50.80   $50.80  
  Purchase #7 $226.98   11.433%   $252.9306   $252.93   $252.95   $252.90  
  7 purchase totals = $704.54       $767.7467   $767.75   $767.75   $767.60