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 $140.42   12.747%   $158.3193   $158.32   $158.30   $158.30  
  Purchase #2 $175.99   10.591%   $194.6291   $194.63   $194.65   $194.60  
  Purchase #3 $219.50   12.722%   $247.4248   $247.42   $247.40   $247.40  
  Purchase #4 $158.81   5.808%   $168.0337   $168.03   $168.05   $168.00  
  Purchase #5 $33.38   7.720%   $35.9569   $35.96   $35.95   $36.00  
  Purchase #6 $174.70   11.267%   $194.3834   $194.38   $194.40   $194.40  
  Purchase #7 $141.52   8.610%   $153.7049   $153.70   $153.70   $153.70  
  7 purchase totals = $1,044.32       $1,152.4521   $1,152.44   $1,152.45   $1,152.40