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 $226.98   5.426%   $239.2959   $239.30   $239.30   $239.30  
  Purchase #2 $217.64   10.172%   $239.7783   $239.78   $239.80   $239.80  
  Purchase #3 $54.79   9.229%   $59.8466   $59.85   $59.85   $59.80  
  Purchase #4 $182.61   11.825%   $204.2036   $204.20   $204.20   $204.20  
  Purchase #5 $17.30   7.704%   $18.6328   $18.63   $18.65   $18.60  
  Purchase #6 $63.87   13.717%   $72.631   $72.63   $72.65   $72.60  
  Purchase #7 $200.92   11.175%   $223.3728   $223.37   $223.35   $223.40  
  7 purchase totals = $964.11       $1,057.7610   $1,057.76   $1,057.80   $1,057.70