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 $243.68   8.547%   $264.5073   $264.51   $264.50   $264.50  
  Purchase #2 $24.49   6.494%   $26.0804   $26.08   $26.10   $26.10  
  Purchase #3 $51.89   7.357%   $55.7075   $55.71   $55.70   $55.70  
  Purchase #4 $203.89   6.161%   $216.4517   $216.45   $216.45   $216.50  
  Purchase #5 $50.62   8.191%   $54.7663   $54.77   $54.75   $54.80  
  Purchase #6 $86.92   5.193%   $91.4338   $91.43   $91.45   $91.40  
  Purchase #7 $215.96   13.451%   $245.0088   $245.01   $245.00   $245.00  
  7 purchase totals = $877.45       $953.9558   $953.96   $953.95   $954.00