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 $54.70   11.747%   $61.1256   $61.13   $61.15   $61.10  
  Purchase #2 $142.92   9.364%   $156.303   $156.30   $156.30   $156.30  
  Purchase #3 $61.95   4.594%   $64.796   $64.80   $64.80   $64.80  
  Purchase #4 $180.73   4.215%   $188.3478   $188.35   $188.35   $188.30  
  Purchase #5 $196.38   10.212%   $216.4343   $216.43   $216.45   $216.40  
  Purchase #6 $43.99   11.247%   $48.9376   $48.94   $48.95   $48.90  
  Purchase #7 $45.44   4.565%   $47.5143   $47.51   $47.50   $47.50  
  7 purchase totals = $726.11       $783.4586   $783.46   $783.50   $783.30