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 $216.75   13.820%   $246.7049   $246.70   $246.70   $246.70  
  Purchase #2 $51.70   13.864%   $58.8677   $58.87   $58.85   $58.90  
  Purchase #3 $74.42   5.226%   $78.3092   $78.31   $78.30   $78.30  
  Purchase #4 $93.30   4.567%   $97.561   $97.56   $97.55   $97.60  
  Purchase #5 $207.65   10.223%   $228.8781   $228.88   $228.90   $228.90  
  Purchase #6 $50.65   6.812%   $54.1003   $54.10   $54.10   $54.10  
  Purchase #7 $202.78   6.111%   $215.1719   $215.17   $215.15   $215.20  
  7 purchase totals = $897.25       $979.5931   $979.59   $979.55   $979.70