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 $58.68   13.213%   $66.4334   $66.43   $66.45   $66.40  
  Purchase #2 $169.41   3.218%   $174.8616   $174.86   $174.85   $174.90  
  Purchase #3 $121.28   9.863%   $133.2418   $133.24   $133.25   $133.20  
  Purchase #4 $95.78   3.680%   $99.3047   $99.30   $99.30   $99.30  
  Purchase #5 $243.59   9.426%   $266.5508   $266.55   $266.55   $266.60  
  Purchase #6 $247.79   12.172%   $277.951   $277.95   $277.95   $278.00  
  Purchase #7 $140.89   12.621%   $158.6717   $158.67   $158.65   $158.70  
  7 purchase totals = $1,077.42       $1,177.0150   $1,177.00   $1,177.00   $1,177.10