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 $74.34   12.520%   $83.6474   $83.65   $83.65   $83.60  
  Purchase #2 $190.48   13.586%   $216.3586   $216.36   $216.35   $216.40  
  Purchase #3 $93.62   8.773%   $101.8333   $101.83   $101.85   $101.80  
  Purchase #4 $247.77   9.425%   $271.1223   $271.12   $271.10   $271.10  
  Purchase #5 $33.34   3.307%   $34.4426   $34.44   $34.45   $34.40  
  Purchase #6 $69.38   9.103%   $75.6957   $75.70   $75.70   $75.70  
  Purchase #7 $230.98   6.731%   $246.5273   $246.53   $246.55   $246.50  
  7 purchase totals = $939.91       $1,029.6272   $1,029.63   $1,029.65   $1,029.50