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 $82.41   13.350%   $93.4117   $93.41   $93.40   $93.40  
  Purchase #2 $189.43   6.554%   $201.8452   $201.85   $201.85   $201.80  
  Purchase #3 $58.45   7.391%   $62.77   $62.77   $62.75   $62.80  
  Purchase #4 $67.52   7.813%   $72.7953   $72.80   $72.80   $72.80  
  Purchase #5 $32.89   3.239%   $33.9553   $33.96   $33.95   $34.00  
  Purchase #6 $102.85   5.729%   $108.7423   $108.74   $108.75   $108.70  
  Purchase #7 $228.32   6.361%   $242.8434   $242.84   $242.85   $242.80  
  7 purchase totals = $761.87       $816.3632   $816.37   $816.35   $816.30