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 $70.95   6.539%   $75.5894   $75.59   $75.60   $75.60  
  Purchase #2 $100.75   11.164%   $111.9977   $112.00   $112.00   $112.00  
  Purchase #3 $56.71   10.667%   $62.7593   $62.76   $62.75   $62.80  
  Purchase #4 $165.43   13.427%   $187.6423   $187.64   $187.65   $187.60  
  Purchase #5 $60.62   9.736%   $66.522   $66.52   $66.50   $66.50  
  Purchase #6 $23.78   7.383%   $25.5357   $25.54   $25.55   $25.50  
  Purchase #7 $149.28   11.217%   $166.0247   $166.02   $166.00   $166.00  
  7 purchase totals = $627.52       $696.0711   $696.07   $696.05   $696.00