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 $232.55   6.217%   $247.0076   $247.01   $247.00   $247.00  
  Purchase #2 $39.29   3.310%   $40.5905   $40.59   $40.60   $40.60  
  Purchase #3 $49.48   11.802%   $55.3196   $55.32   $55.30   $55.30  
  Purchase #4 $175.38   4.285%   $182.895   $182.90   $182.90   $182.90  
  Purchase #5 $91.57   6.214%   $97.2602   $97.26   $97.25   $97.30  
  Purchase #6 $184.76   9.311%   $201.963   $201.96   $201.95   $202.00  
  Purchase #7 $55.57   4.395%   $58.0123   $58.01   $58.00   $58.00  
  7 purchase totals = $828.60       $883.0482   $883.05   $883.00   $883.10