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 $204.30   5.261%   $215.0482   $215.05   $215.05   $215.00  
  Purchase #2 $31.38   11.308%   $34.9285   $34.93   $34.95   $34.90  
  Purchase #3 $98.52   9.486%   $107.8656   $107.87   $107.85   $107.90  
  Purchase #4 $138.77   8.505%   $150.5724   $150.57   $150.55   $150.60  
  Purchase #5 $150.72   10.202%   $166.0965   $166.10   $166.10   $166.10  
  Purchase #6 $193.75   9.104%   $211.389   $211.39   $211.40   $211.40  
  Purchase #7 $70.38   5.539%   $74.2783   $74.28   $74.30   $74.30  
  7 purchase totals = $887.82       $960.1785   $960.19   $960.20   $960.20