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 $224.88   10.570%   $248.6498   $248.65   $248.65   $248.60  
  Purchase #2 $146.29   6.454%   $155.7316   $155.73   $155.75   $155.70  
  Purchase #3 $165.63   12.544%   $186.4066   $186.41   $186.40   $186.40  
  Purchase #4 $239.54   5.831%   $253.5076   $253.51   $253.50   $253.50  
  Purchase #5 $213.71   9.228%   $233.4312   $233.43   $233.45   $233.40  
  Purchase #6 $172.92   4.455%   $180.6236   $180.62   $180.60   $180.60  
  Purchase #7 $33.43   8.499%   $36.2712   $36.27   $36.25   $36.30  
  7 purchase totals = $1,196.40       $1,294.6216   $1,294.62   $1,294.60   $1,294.50