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 $59.96   4.617%   $62.7284   $62.73   $62.75   $62.70  
  Purchase #2 $150.94   9.357%   $165.0635   $165.06   $165.05   $165.10  
  Purchase #3 $27.86   7.873%   $30.0534   $30.05   $30.05   $30.10  
  Purchase #4 $90.65   6.326%   $96.3845   $96.38   $96.40   $96.40  
  Purchase #5 $53.96   5.186%   $56.7584   $56.76   $56.75   $56.80  
  Purchase #6 $76.96   4.535%   $80.4501   $80.45   $80.45   $80.50  
  Purchase #7 $114.98   5.743%   $121.5833   $121.58   $121.60   $121.60  
  7 purchase totals = $575.31       $613.0216   $613.01   $613.05   $613.20