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 $250.35   10.113%   $275.6679   $275.67   $275.65   $275.70  
  Purchase #2 $23.77   3.670%   $24.6424   $24.64   $24.65   $24.60  
  Purchase #3 $54.88   8.833%   $59.7276   $59.73   $59.75   $59.70  
  Purchase #4 $250.48   7.819%   $270.065   $270.07   $270.05   $270.10  
  Purchase #5 $10.75   13.710%   $12.2238   $12.22   $12.20   $12.20  
  Purchase #6 $64.44   7.325%   $69.1602   $69.16   $69.15   $69.20  
  Purchase #7 $218.29   11.642%   $243.7033   $243.70   $243.70   $243.70  
  7 purchase totals = $872.96       $955.1902   $955.19   $955.15   $955.20