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 $224.98   8.596%   $244.3193   $244.32   $244.30   $244.30  
  Purchase #2 $156.90   11.325%   $174.6689   $174.67   $174.65   $174.70  
  Purchase #3 $45.31   10.146%   $49.9072   $49.91   $49.90   $49.90  
  Purchase #4 $233.48   10.317%   $257.5681   $257.57   $257.55   $257.60  
  Purchase #5 $192.29   7.507%   $206.7252   $206.73   $206.75   $206.70  
  Purchase #6 $51.34   11.197%   $57.0885   $57.09   $57.10   $57.10  
  Purchase #7 $60.83   5.121%   $63.9451   $63.95   $63.95   $63.90  
  7 purchase totals = $965.13       $1,054.2223   $1,054.24   $1,054.20   $1,054.20