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 $40.27   10.782%   $44.6119   $44.61   $44.60   $44.60  
  Purchase #2 $141.71   13.491%   $160.8281   $160.83   $160.85   $160.80  
  Purchase #3 $71.85   4.417%   $75.0236   $75.02   $75.00   $75.00  
  Purchase #4 $112.81   11.363%   $125.6286   $125.63   $125.65   $125.60  
  Purchase #5 $211.68   8.322%   $229.296   $229.30   $229.30   $229.30  
  Purchase #6 $183.74   12.371%   $206.4705   $206.47   $206.45   $206.50  
  Purchase #7 $206.44   13.765%   $234.8565   $234.86   $234.85   $234.90  
  7 purchase totals = $968.50       $1,076.7152   $1,076.72   $1,076.70   $1,076.70