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 $32.52   13.671%   $36.9658   $36.97   $36.95   $37.00  
  Purchase #2 $187.96   10.218%   $207.1658   $207.17   $207.15   $207.20  
  Purchase #3 $45.35   9.745%   $49.7694   $49.77   $49.75   $49.80  
  Purchase #4 $127.95   12.323%   $143.7173   $143.72   $143.70   $143.70  
  Purchase #5 $113.54   5.539%   $119.829   $119.83   $119.85   $119.80  
  Purchase #6 $73.84   11.751%   $82.5169   $82.52   $82.50   $82.50  
  Purchase #7 $154.96   5.160%   $162.9559   $162.96   $162.95   $163.00  
  7 purchase totals = $736.12       $802.9201   $802.94   $802.85   $803.00