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 $67.84   11.433%   $75.5961   $75.60   $75.60   $75.60  
  Purchase #2 $123.84   9.564%   $135.6841   $135.68   $135.70   $135.70  
  Purchase #3 $165.40   5.432%   $174.3845   $174.38   $174.40   $174.40  
  Purchase #4 $43.73   8.275%   $47.3487   $47.35   $47.35   $47.30  
  Purchase #5 $44.77   6.235%   $47.5614   $47.56   $47.55   $47.60  
  Purchase #6 $221.53   4.790%   $232.1413   $232.14   $232.15   $232.10  
  Purchase #7 $168.72   4.472%   $176.2652   $176.27   $176.25   $176.30  
  7 purchase totals = $835.83       $888.9813   $888.98   $889.00   $889.00