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 $31.39   12.398%   $35.2817   $35.28   $35.30   $35.30  
  Purchase #2 $54.36   8.373%   $58.9116   $58.91   $58.90   $58.90  
  Purchase #3 $169.46   8.326%   $183.5692   $183.57   $183.55   $183.60  
  Purchase #4 $137.38   13.555%   $156.0019   $156.00   $156.00   $156.00  
  Purchase #5 $43.73   8.158%   $47.2975   $47.30   $47.30   $47.30  
  Purchase #6 $94.66   10.850%   $104.9306   $104.93   $104.95   $104.90  
  Purchase #7 $157.93   10.544%   $174.5821   $174.58   $174.60   $174.60  
  7 purchase totals = $688.91       $760.5746   $760.57   $760.60   $760.60