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 $94.25   8.152%   $101.9333   $101.93   $101.95   $101.90  
  Purchase #2 $247.31   8.758%   $268.9694   $268.97   $268.95   $269.00  
  Purchase #3 $129.48   8.358%   $140.3019   $140.30   $140.30   $140.30  
  Purchase #4 $48.96   5.585%   $51.6944   $51.69   $51.70   $51.70  
  Purchase #5 $42.33   5.320%   $44.582   $44.58   $44.60   $44.60  
  Purchase #6 $195.36   5.617%   $206.3334   $206.33   $206.35   $206.30  
  Purchase #7 $183.84   5.449%   $193.8574   $193.86   $193.85   $193.90  
  7 purchase totals = $941.53       $1,007.6718   $1,007.66   $1,007.70   $1,007.70