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 $55.34   12.616%   $62.3217   $62.32   $62.30   $62.30  
  Purchase #2 $179.91   10.370%   $198.5667   $198.57   $198.55   $198.60  
  Purchase #3 $63.49   5.865%   $67.2137   $67.21   $67.20   $67.20  
  Purchase #4 $14.80   7.331%   $15.885   $15.89   $15.90   $15.90  
  Purchase #5 $243.47   5.482%   $256.817   $256.82   $256.80   $256.80  
  Purchase #6 $113.44   11.811%   $126.8384   $126.84   $126.85   $126.80  
  Purchase #7 $175.44   7.348%   $188.3313   $188.33   $188.35   $188.30  
  7 purchase totals = $845.89       $915.9738   $915.98   $915.95   $915.90