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 $62.47   6.495%   $66.5274   $66.53   $66.55   $66.50  
  Purchase #2 $148.77   11.759%   $166.2639   $166.26   $166.25   $166.30  
  Purchase #3 $217.32   11.739%   $242.8312   $242.83   $242.85   $242.80  
  Purchase #4 $73.40   3.142%   $75.7062   $75.71   $75.70   $75.70  
  Purchase #5 $173.44   9.269%   $189.5162   $189.52   $189.50   $189.50  
  Purchase #6 $26.95   11.159%   $29.9574   $29.96   $29.95   $30.00  
  Purchase #7 $76.94   10.775%   $85.2303   $85.23   $85.25   $85.20  
  7 purchase totals = $779.29       $856.0326   $856.04   $856.05   $856.00