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 $42.80   4.564%   $44.7534   $44.75   $44.75   $44.80  
  Purchase #2 $201.79   11.655%   $225.3086   $225.31   $225.30   $225.30  
  Purchase #3 $246.82   5.761%   $261.0393   $261.04   $261.05   $261.00  
  Purchase #4 $62.47   13.700%   $71.0284   $71.03   $71.05   $71.00  
  Purchase #5 $238.28   7.390%   $255.8889   $255.89   $255.90   $255.90  
  Purchase #6 $183.61   11.352%   $204.4534   $204.45   $204.45   $204.50  
  Purchase #7 $23.28   6.271%   $24.7399   $24.74   $24.75   $24.70  
  7 purchase totals = $999.05       $1,087.2119   $1,087.21   $1,087.25   $1,087.20