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 $232.75   13.864%   $265.0185   $265.02   $265.00   $265.00  
  Purchase #2 $26.63   12.176%   $29.8725   $29.87   $29.85   $29.90  
  Purchase #3 $59.69   3.841%   $61.9827   $61.98   $62.00   $62.00  
  Purchase #4 $213.89   5.112%   $224.8241   $224.82   $224.80   $224.80  
  Purchase #5 $197.38   10.378%   $217.8641   $217.86   $217.85   $217.90  
  Purchase #6 $69.96   6.294%   $74.3633   $74.36   $74.35   $74.40  
  Purchase #7 $105.59   13.839%   $120.2026   $120.20   $120.20   $120.20  
  7 purchase totals = $905.89       $994.1278   $994.11   $994.05   $994.20