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 $227.62   7.241%   $244.102   $244.10   $244.10   $244.10  
  Purchase #2 $230.92   8.247%   $249.964   $249.96   $249.95   $250.00  
  Purchase #3 $134.34   13.595%   $152.6035   $152.60   $152.60   $152.60  
  Purchase #4 $24.58   12.508%   $27.6545   $27.65   $27.65   $27.70  
  Purchase #5 $23.57   5.436%   $24.8513   $24.85   $24.85   $24.90  
  Purchase #6 $83.37   6.316%   $88.6356   $88.64   $88.65   $88.60  
  Purchase #7 $240.36   13.712%   $273.3182   $273.32   $273.30   $273.30  
  7 purchase totals = $964.76       $1,061.1291   $1,061.12   $1,061.10   $1,061.20