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 $232.65   7.470%   $250.029   $250.03   $250.05   $250.00  
  Purchase #2 $21.97   3.340%   $22.7038   $22.70   $22.70   $22.70  
  Purchase #3 $96.39   8.797%   $104.8694   $104.87   $104.85   $104.90  
  Purchase #4 $48.42   8.170%   $52.3759   $52.38   $52.40   $52.40  
  Purchase #5 $199.92   7.182%   $214.2783   $214.28   $214.30   $214.30  
  Purchase #6 $236.39   7.798%   $254.8237   $254.82   $254.80   $254.80  
  Purchase #7 $212.61   10.603%   $235.153   $235.15   $235.15   $235.20  
  7 purchase totals = $1,048.35       $1,134.2331   $1,134.23   $1,134.25   $1,134.30