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 $24.87   4.593%   $26.0123   $26.01   $26.00   $26.00  
  Purchase #2 $95.91   6.292%   $101.9447   $101.94   $101.95   $101.90  
  Purchase #3 $122.53   13.488%   $139.0568   $139.06   $139.05   $139.10  
  Purchase #4 $88.52   9.322%   $96.7718   $96.77   $96.75   $96.80  
  Purchase #5 $135.40   8.316%   $146.6599   $146.66   $146.65   $146.70  
  Purchase #6 $241.60   6.598%   $257.5408   $257.54   $257.55   $257.50  
  Purchase #7 $31.72   8.840%   $34.524   $34.52   $34.50   $34.50  
  7 purchase totals = $740.55       $802.5103   $802.50   $802.45   $802.50