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 $77.41   9.293%   $84.6037   $84.60   $84.60   $84.60  
  Purchase #2 $116.52   6.732%   $124.3641   $124.36   $124.35   $124.40  
  Purchase #3 $92.78   10.719%   $102.7251   $102.73   $102.75   $102.70  
  Purchase #4 $236.42   13.297%   $267.8568   $267.86   $267.85   $267.90  
  Purchase #5 $168.64   3.805%   $175.0568   $175.06   $175.05   $175.10  
  Purchase #6 $81.91   13.588%   $93.0399   $93.04   $93.05   $93.00  
  Purchase #7 $96.70   5.367%   $101.8899   $101.89   $101.90   $101.90  
  7 purchase totals = $870.38       $949.5363   $949.54   $949.55   $949.60