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 $204.88   5.230%   $215.5952   $215.60   $215.60   $215.60  
  Purchase #2 $30.55   11.491%   $34.0605   $34.06   $34.05   $34.10  
  Purchase #3 $48.78   10.265%   $53.7873   $53.79   $53.80   $53.80  
  Purchase #4 $43.46   5.566%   $45.879   $45.88   $45.90   $45.90  
  Purchase #5 $225.48   5.276%   $237.3763   $237.38   $237.40   $237.40  
  Purchase #6 $58.39   10.872%   $64.7382   $64.74   $64.75   $64.70  
  Purchase #7 $26.31   3.216%   $27.1561   $27.16   $27.15   $27.20  
  7 purchase totals = $637.85       $678.5926   $678.61   $678.65   $678.70