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 $67.38   11.813%   $75.3396   $75.34   $75.35   $75.30  
  Purchase #2 $87.43   5.553%   $92.285   $92.29   $92.30   $92.30  
  Purchase #3 $217.73   8.867%   $237.0361   $237.04   $237.05   $237.00  
  Purchase #4 $110.91   3.396%   $114.6765   $114.68   $114.70   $114.70  
  Purchase #5 $109.71   3.277%   $113.3052   $113.31   $113.30   $113.30  
  Purchase #6 $175.52   9.270%   $191.7907   $191.79   $191.80   $191.80  
  Purchase #7 $213.70   8.589%   $232.0547   $232.05   $232.05   $232.10  
  7 purchase totals = $982.38       $1,056.4878   $1,056.50   $1,056.55   $1,056.50