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 $54.44   13.342%   $61.7034   $61.70   $61.70   $61.70  
  Purchase #2 $202.29   5.510%   $213.4362   $213.44   $213.45   $213.40  
  Purchase #3 $90.56   3.663%   $93.8772   $93.88   $93.90   $93.90  
  Purchase #4 $128.42   5.428%   $135.3906   $135.39   $135.40   $135.40  
  Purchase #5 $116.98   4.874%   $122.6816   $122.68   $122.70   $122.70  
  Purchase #6 $56.59   13.582%   $64.2761   $64.28   $64.30   $64.30  
  Purchase #7 $250.28   11.185%   $278.2738   $278.27   $278.25   $278.30  
  7 purchase totals = $899.56       $969.6389   $969.64   $969.70   $969.70