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 $84.54   11.104%   $93.9273   $93.93   $93.95   $93.90  
  Purchase #2 $16.59   12.111%   $18.5992   $18.60   $18.60   $18.60  
  Purchase #3 $97.92   12.421%   $110.0826   $110.08   $110.10   $110.10  
  Purchase #4 $209.39   11.580%   $233.6374   $233.64   $233.65   $233.60  
  Purchase #5 $109.82   11.376%   $122.3131   $122.31   $122.30   $122.30  
  Purchase #6 $39.39   11.456%   $43.9025   $43.90   $43.90   $43.90  
  Purchase #7 $233.38   7.159%   $250.0877   $250.09   $250.10   $250.10  
  7 purchase totals = $791.03       $872.5498   $872.55   $872.60   $872.50