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 $29.25   10.849%   $32.4233   $32.42   $32.40   $32.40  
  Purchase #2 $174.76   13.289%   $197.9839   $197.98   $198.00   $198.00  
  Purchase #3 $244.46   4.109%   $254.5049   $254.50   $254.50   $254.50  
  Purchase #4 $115.54   12.443%   $129.9166   $129.92   $129.90   $129.90  
  Purchase #5 $11.36   12.120%   $12.7368   $12.74   $12.75   $12.70  
  Purchase #6 $167.57   11.217%   $186.3663   $186.37   $186.35   $186.40  
  Purchase #7 $220.54   12.355%   $247.7877   $247.79   $247.80   $247.80  
  7 purchase totals = $963.48       $1,061.7195   $1,061.72   $1,061.70   $1,061.70