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 $243.81   10.177%   $268.6225   $268.62   $268.60   $268.60  
  Purchase #2 $176.91   4.440%   $184.7648   $184.76   $184.75   $184.80  
  Purchase #3 $11.41   9.105%   $12.4489   $12.45   $12.45   $12.40  
  Purchase #4 $218.79   12.122%   $245.3117   $245.31   $245.30   $245.30  
  Purchase #5 $152.98   5.357%   $161.1751   $161.18   $161.20   $161.20  
  Purchase #6 $24.30   5.656%   $25.6744   $25.67   $25.65   $25.70  
  Purchase #7 $66.70   4.332%   $69.5894   $69.59   $69.60   $69.60  
  7 purchase totals = $894.90       $967.5868   $967.58   $967.55   $967.60