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 $95.68   13.795%   $108.8791   $108.88   $108.90   $108.90  
  Purchase #2 $93.65   4.263%   $97.6423   $97.64   $97.65   $97.60  
  Purchase #3 $89.73   7.569%   $96.5217   $96.52   $96.50   $96.50  
  Purchase #4 $218.36   7.140%   $233.9509   $233.95   $233.95   $234.00  
  Purchase #5 $52.58   3.667%   $54.5081   $54.51   $54.50   $54.50  
  Purchase #6 $123.86   9.598%   $135.7481   $135.75   $135.75   $135.70  
  Purchase #7 $222.57   11.103%   $247.2819   $247.28   $247.30   $247.30  
  7 purchase totals = $896.43       $974.5321   $974.53   $974.55   $974.50