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 $24.72   5.469%   $26.0719   $26.07   $26.05   $26.10  
  Purchase #2 $237.97   5.463%   $250.9703   $250.97   $250.95   $251.00  
  Purchase #3 $104.63   11.194%   $116.3423   $116.34   $116.35   $116.30  
  Purchase #4 $94.75   6.459%   $100.8699   $100.87   $100.85   $100.90  
  Purchase #5 $80.61   10.813%   $89.3264   $89.33   $89.35   $89.30  
  Purchase #6 $217.94   13.675%   $247.7433   $247.74   $247.75   $247.70  
  Purchase #7 $172.40   12.436%   $193.8397   $193.84   $193.85   $193.80  
  7 purchase totals = $933.02       $1,025.1638   $1,025.16   $1,025.15   $1,025.10