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 $200.36   3.571%   $207.5149   $207.51   $207.50   $207.50  
  Purchase #2 $110.64   6.256%   $117.5616   $117.56   $117.55   $117.60  
  Purchase #3 $46.93   10.179%   $51.707   $51.71   $51.70   $51.70  
  Purchase #4 $239.76   8.185%   $259.3844   $259.38   $259.40   $259.40  
  Purchase #5 $61.91   8.438%   $67.134   $67.13   $67.15   $67.10  
  Purchase #6 $127.31   10.132%   $140.209   $140.21   $140.20   $140.20  
  Purchase #7 $202.48   8.713%   $220.1221   $220.12   $220.10   $220.10  
  7 purchase totals = $989.39       $1,063.6330   $1,063.62   $1,063.60   $1,063.60