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 $114.98   7.589%   $123.7058   $123.71   $123.70   $123.70  
  Purchase #2 $86.25   8.179%   $93.3044   $93.30   $93.30   $93.30  
  Purchase #3 $152.88   4.330%   $159.4997   $159.50   $159.50   $159.50  
  Purchase #4 $247.49   8.679%   $268.9697   $268.97   $268.95   $269.00  
  Purchase #5 $170.92   4.855%   $179.2182   $179.22   $179.20   $179.20  
  Purchase #6 $118.30   10.173%   $130.3347   $130.33   $130.35   $130.30  
  Purchase #7 $82.69   8.390%   $89.6277   $89.63   $89.65   $89.60  
  7 purchase totals = $973.51       $1,044.6602   $1,044.66   $1,044.65   $1,044.60