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 $49.41   6.754%   $52.7472   $52.75   $52.75   $52.70  
  Purchase #2 $229.50   12.103%   $257.2764   $257.28   $257.30   $257.30  
  Purchase #3 $50.75   12.343%   $57.0141   $57.01   $57.00   $57.00  
  Purchase #4 $46.36   8.242%   $50.181   $50.18   $50.20   $50.20  
  Purchase #5 $135.26   10.848%   $149.933   $149.93   $149.95   $149.90  
  Purchase #6 $184.74   5.501%   $194.9025   $194.90   $194.90   $194.90  
  Purchase #7 $128.62   5.325%   $135.469   $135.47   $135.45   $135.50  
  7 purchase totals = $824.64       $897.5232   $897.52   $897.55   $897.50