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 $152.81   9.781%   $167.7563   $167.76   $167.75   $167.80  
  Purchase #2 $234.43   5.536%   $247.408   $247.41   $247.40   $247.40  
  Purchase #3 $216.58   4.305%   $225.9038   $225.90   $225.90   $225.90  
  Purchase #4 $29.29   10.360%   $32.3244   $32.32   $32.30   $32.30  
  Purchase #5 $244.62   12.628%   $275.5106   $275.51   $275.50   $275.50  
  Purchase #6 $233.48   5.725%   $246.8467   $246.85   $246.85   $246.80  
  Purchase #7 $184.33   9.297%   $201.4672   $201.47   $201.45   $201.50  
  7 purchase totals = $1,295.54       $1,397.2170   $1,397.22   $1,397.15   $1,397.20