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 $222.49   9.473%   $243.5665   $243.57   $243.55   $243.60  
  Purchase #2 $195.67   4.311%   $204.1053   $204.11   $204.10   $204.10  
  Purchase #3 $10.72   11.709%   $11.9752   $11.98   $12.00   $12.00  
  Purchase #4 $13.91   12.265%   $15.6161   $15.62   $15.60   $15.60  
  Purchase #5 $9.28   10.611%   $10.2647   $10.26   $10.25   $10.30  
  Purchase #6 $162.33   11.193%   $180.4996   $180.50   $180.50   $180.50  
  Purchase #7 $113.65   12.257%   $127.5801   $127.58   $127.60   $127.60  
  7 purchase totals = $728.05       $793.6075   $793.62   $793.60   $793.70