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 $228.63   9.603%   $250.5853   $250.59   $250.60   $250.60  
  Purchase #2 $180.45   12.377%   $202.7843   $202.78   $202.80   $202.80  
  Purchase #3 $207.70   13.205%   $235.1268   $235.13   $235.15   $235.10  
  Purchase #4 $132.96   12.436%   $149.4949   $149.49   $149.50   $149.50  
  Purchase #5 $110.63   13.390%   $125.4434   $125.44   $125.45   $125.40  
  Purchase #6 $140.80   3.297%   $145.4422   $145.44   $145.45   $145.40  
  Purchase #7 $98.76   3.142%   $101.863   $101.86   $101.85   $101.90  
  7 purchase totals = $1,099.93       $1,210.7399   $1,210.73   $1,210.80   $1,210.70