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 $64.66   7.136%   $69.2741   $69.27   $69.25   $69.30  
  Purchase #2 $239.65   9.354%   $262.0669   $262.07   $262.05   $262.10  
  Purchase #3 $73.25   13.701%   $83.286   $83.29   $83.30   $83.30  
  Purchase #4 $193.86   9.648%   $212.5636   $212.56   $212.55   $212.60  
  Purchase #5 $148.65   9.474%   $162.7331   $162.73   $162.75   $162.70  
  Purchase #6 $19.31   5.129%   $20.3004   $20.30   $20.30   $20.30  
  Purchase #7 $48.95   8.813%   $53.264   $53.26   $53.25   $53.30  
  7 purchase totals = $788.33       $863.4881   $863.48   $863.45   $863.60