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 $60.79   7.796%   $65.5292   $65.53   $65.55   $65.50  
  Purchase #2 $152.74   3.426%   $157.9729   $157.97   $157.95   $158.00  
  Purchase #3 $233.32   11.258%   $259.5872   $259.59   $259.60   $259.60  
  Purchase #4 $165.43   3.612%   $171.4053   $171.41   $171.40   $171.40  
  Purchase #5 $230.71   10.126%   $254.0717   $254.07   $254.05   $254.10  
  Purchase #6 $20.95   10.358%   $23.12   $23.12   $23.10   $23.10  
  Purchase #7 $83.42   6.600%   $88.9257   $88.93   $88.95   $88.90  
  7 purchase totals = $947.36       $1,020.6120   $1,020.62   $1,020.60   $1,020.60