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 $59.76   9.482%   $65.4264   $65.43   $65.45   $65.40  
  Purchase #2 $224.89   11.453%   $250.6467   $250.65   $250.65   $250.60  
  Purchase #3 $192.29   4.789%   $201.4988   $201.50   $201.50   $201.50  
  Purchase #4 $31.28   4.215%   $32.5985   $32.60   $32.60   $32.60  
  Purchase #5 $168.89   5.630%   $178.3985   $178.40   $178.40   $178.40  
  Purchase #6 $144.36   11.173%   $160.4893   $160.49   $160.50   $160.50  
  Purchase #7 $25.57   3.832%   $26.5498   $26.55   $26.55   $26.50  
  7 purchase totals = $847.04       $915.6080   $915.62   $915.65   $915.50