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 $210.74   13.621%   $239.4449   $239.44   $239.45   $239.40  
  Purchase #2 $246.61   5.140%   $259.2858   $259.29   $259.30   $259.30  
  Purchase #3 $194.80   11.224%   $216.6644   $216.66   $216.65   $216.70  
  Purchase #4 $74.82   9.346%   $81.8127   $81.81   $81.80   $81.80  
  Purchase #5 $250.75   11.301%   $279.0873   $279.09   $279.10   $279.10  
  Purchase #6 $44.87   3.436%   $46.4117   $46.41   $46.40   $46.40  
  Purchase #7 $40.92   5.339%   $43.1047   $43.10   $43.10   $43.10  
  7 purchase totals = $1,063.51       $1,165.8115   $1,165.80   $1,165.80   $1,165.80