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 $46.84   7.334%   $50.2752   $50.28   $50.30   $50.30  
  Purchase #2 $211.75   13.301%   $239.9149   $239.91   $239.90   $239.90  
  Purchase #3 $163.29   13.111%   $184.699   $184.70   $184.70   $184.70  
  Purchase #4 $60.74   11.717%   $67.8569   $67.86   $67.85   $67.90  
  Purchase #5 $178.96   3.157%   $184.6098   $184.61   $184.60   $184.60  
  Purchase #6 $163.74   7.142%   $175.4343   $175.43   $175.45   $175.40  
  Purchase #7 $41.96   10.562%   $46.3918   $46.39   $46.40   $46.40  
  7 purchase totals = $867.28       $949.1819   $949.18   $949.20   $949.20