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 $62.57   6.330%   $66.5307   $66.53   $66.55   $66.50  
  Purchase #2 $173.83   12.656%   $195.8299   $195.83   $195.85   $195.80  
  Purchase #3 $182.91   9.390%   $200.0852   $200.09   $200.10   $200.10  
  Purchase #4 $203.71   5.873%   $215.6739   $215.67   $215.65   $215.70  
  Purchase #5 $49.72   9.337%   $54.3624   $54.36   $54.35   $54.40  
  Purchase #6 $160.72   10.452%   $177.5185   $177.52   $177.50   $177.50  
  Purchase #7 $144.93   8.830%   $157.7273   $157.73   $157.75   $157.70  
  7 purchase totals = $978.39       $1,067.7279   $1,067.73   $1,067.75   $1,067.70