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 $51.59   8.523%   $55.987   $55.99   $56.00   $56.00  
  Purchase #2 $127.28   9.172%   $138.9541   $138.95   $138.95   $139.00  
  Purchase #3 $187.66   7.844%   $202.3801   $202.38   $202.40   $202.40  
  Purchase #4 $96.69   6.823%   $103.2872   $103.29   $103.30   $103.30  
  Purchase #5 $90.57   8.271%   $98.061   $98.06   $98.05   $98.10  
  Purchase #6 $148.62   11.751%   $166.0843   $166.08   $166.10   $166.10  
  Purchase #7 $58.95   5.107%   $61.9606   $61.96   $61.95   $62.00  
  7 purchase totals = $761.36       $826.7143   $826.71   $826.75   $826.90