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 $38.53   13.596%   $43.7685   $43.77   $43.75   $43.80  
  Purchase #2 $88.40   7.417%   $94.9566   $94.96   $94.95   $95.00  
  Purchase #3 $16.98   7.120%   $18.189   $18.19   $18.20   $18.20  
  Purchase #4 $114.38   9.300%   $125.0173   $125.02   $125.00   $125.00  
  Purchase #5 $159.52   7.127%   $170.889   $170.89   $170.90   $170.90  
  Purchase #6 $210.83   5.757%   $222.9675   $222.97   $222.95   $223.00  
  Purchase #7 $242.28   3.395%   $250.5054   $250.51   $250.50   $250.50  
  7 purchase totals = $870.92       $926.2933   $926.31   $926.25   $926.40