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 $206.42   13.113%   $233.4879   $233.49   $233.50   $233.50  
  Purchase #2 $216.56   3.263%   $223.6264   $223.63   $223.65   $223.60  
  Purchase #3 $21.75   5.545%   $22.956   $22.96   $22.95   $23.00  
  Purchase #4 $177.59   5.651%   $187.6256   $187.63   $187.65   $187.60  
  Purchase #5 $115.92   7.581%   $124.7079   $124.71   $124.70   $124.70  
  Purchase #6 $218.25   7.677%   $235.0051   $235.01   $235.00   $235.00  
  Purchase #7 $45.63   4.357%   $47.6181   $47.62   $47.60   $47.60  
  7 purchase totals = $1,002.12       $1,075.0270   $1,075.05   $1,075.05   $1,075.00