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 $90.40   10.650%   $100.0276   $100.03   $100.05   $100.00  
  Purchase #2 $210.41   3.694%   $218.1825   $218.18   $218.20   $218.20  
  Purchase #3 $235.98   10.662%   $261.1402   $261.14   $261.15   $261.10  
  Purchase #4 $169.31   11.337%   $188.5047   $188.50   $188.50   $188.50  
  Purchase #5 $165.91   13.181%   $187.7786   $187.78   $187.80   $187.80  
  Purchase #6 $216.48   10.445%   $239.0913   $239.09   $239.10   $239.10  
  Purchase #7 $186.31   13.507%   $211.4749   $211.47   $211.45   $211.50  
  7 purchase totals = $1,274.80       $1,406.1998   $1,406.19   $1,406.25   $1,406.20