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 $218.32   3.841%   $226.7057   $226.71   $226.70   $226.70  
  Purchase #2 $104.46   13.690%   $118.7606   $118.76   $118.75   $118.80  
  Purchase #3 $110.59   4.165%   $115.1961   $115.20   $115.20   $115.20  
  Purchase #4 $207.88   4.689%   $217.6275   $217.63   $217.65   $217.60  
  Purchase #5 $106.81   11.819%   $119.4339   $119.43   $119.45   $119.40  
  Purchase #6 $30.54   6.316%   $32.4689   $32.47   $32.45   $32.50  
  Purchase #7 $174.59   4.196%   $181.9158   $181.92   $181.90   $181.90  
  7 purchase totals = $953.19       $1,012.1085   $1,012.12   $1,012.10   $1,012.10