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 $48.39   9.287%   $52.884   $52.88   $52.90   $52.90  
  Purchase #2 $224.91   12.363%   $252.7156   $252.72   $252.70   $252.70  
  Purchase #3 $56.48   4.343%   $58.9329   $58.93   $58.95   $58.90  
  Purchase #4 $170.48   4.848%   $178.7449   $178.74   $178.75   $178.70  
  Purchase #5 $115.84   13.111%   $131.0278   $131.03   $131.05   $131.00  
  Purchase #6 $142.28   13.580%   $161.6016   $161.60   $161.60   $161.60  
  Purchase #7 $200.54   3.756%   $208.0723   $208.07   $208.05   $208.10  
  7 purchase totals = $958.92       $1,043.9791   $1,043.97   $1,044.00   $1,043.90