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 $89.42   5.350%   $94.204   $94.20   $94.20   $94.20  
  Purchase #2 $229.48   6.773%   $245.0227   $245.02   $245.00   $245.00  
  Purchase #3 $94.96   4.484%   $99.218   $99.22   $99.20   $99.20  
  Purchase #4 $30.99   10.626%   $34.283   $34.28   $34.30   $34.30  
  Purchase #5 $224.51   4.716%   $235.0979   $235.10   $235.10   $235.10  
  Purchase #6 $195.59   3.213%   $201.8743   $201.87   $201.85   $201.90  
  Purchase #7 $60.30   13.402%   $68.3814   $68.38   $68.40   $68.40  
  7 purchase totals = $925.25       $978.0813   $978.07   $978.05   $978.10