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 $29.76   9.132%   $32.4777   $32.48   $32.50   $32.50  
  Purchase #2 $212.43   3.329%   $219.5018   $219.50   $219.50   $219.50  
  Purchase #3 $117.53   13.119%   $132.9488   $132.95   $132.95   $132.90  
  Purchase #4 $169.58   6.587%   $180.7502   $180.75   $180.75   $180.80  
  Purchase #5 $56.93   9.874%   $62.5513   $62.55   $62.55   $62.60  
  Purchase #6 $195.64   5.488%   $206.3767   $206.38   $206.40   $206.40  
  Purchase #7 $246.96   4.581%   $258.2732   $258.27   $258.25   $258.30  
  7 purchase totals = $1,028.83       $1,092.8797   $1,092.88   $1,092.90   $1,093.00