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 $23.95   9.543%   $26.2355   $26.24   $26.25   $26.20  
  Purchase #2 $124.86   5.585%   $131.8334   $131.83   $131.85   $131.80  
  Purchase #3 $167.29   3.266%   $172.7537   $172.75   $172.75   $172.80  
  Purchase #4 $55.32   10.373%   $61.0583   $61.06   $61.05   $61.10  
  Purchase #5 $147.65   3.698%   $153.1101   $153.11   $153.10   $153.10  
  Purchase #6 $152.41   9.582%   $167.0139   $167.01   $167.00   $167.00  
  Purchase #7 $162.63   13.591%   $184.733   $184.73   $184.75   $184.70  
  7 purchase totals = $834.11       $896.7379   $896.73   $896.75   $896.70