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 $238.98   8.633%   $259.6111   $259.61   $259.60   $259.60  
  Purchase #2 $198.26   6.186%   $210.5244   $210.52   $210.50   $210.50  
  Purchase #3 $239.89   6.219%   $254.8088   $254.81   $254.80   $254.80  
  Purchase #4 $60.47   13.567%   $68.674   $68.67   $68.65   $68.70  
  Purchase #5 $14.50   12.343%   $16.2897   $16.29   $16.30   $16.30  
  Purchase #6 $114.73   9.389%   $125.502   $125.50   $125.50   $125.50  
  Purchase #7 $72.41   7.518%   $77.8538   $77.85   $77.85   $77.90  
  7 purchase totals = $939.24       $1,013.2638   $1,013.25   $1,013.20   $1,013.30