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 $68.31   12.647%   $76.9492   $76.95   $76.95   $76.90  
  Purchase #2 $247.80   6.243%   $263.2702   $263.27   $263.25   $263.30  
  Purchase #3 $88.89   6.569%   $94.7292   $94.73   $94.75   $94.70  
  Purchase #4 $156.79   5.401%   $165.2582   $165.26   $165.25   $165.30  
  Purchase #5 $29.83   9.258%   $32.5917   $32.59   $32.60   $32.60  
  Purchase #6 $134.82   12.295%   $151.3961   $151.40   $151.40   $151.40  
  Purchase #7 $169.77   3.746%   $176.1296   $176.13   $176.15   $176.10  
  7 purchase totals = $896.21       $960.3242   $960.33   $960.35   $960.30