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 $58.56   8.753%   $63.6858   $63.69   $63.70   $63.70  
  Purchase #2 $43.41   11.401%   $48.3592   $48.36   $48.35   $48.40  
  Purchase #3 $97.42   7.637%   $104.86   $104.86   $104.85   $104.90  
  Purchase #4 $74.63   9.859%   $81.9878   $81.99   $82.00   $82.00  
  Purchase #5 $147.69   12.128%   $165.6018   $165.60   $165.60   $165.60  
  Purchase #6 $105.45   10.820%   $116.8597   $116.86   $116.85   $116.90  
  Purchase #7 $201.47   6.643%   $214.8537   $214.85   $214.85   $214.90  
  7 purchase totals = $728.63       $796.2080   $796.21   $796.20   $796.40