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 $241.63   11.432%   $269.2531   $269.25   $269.25   $269.30  
  Purchase #2 $118.98   12.106%   $133.3837   $133.38   $133.40   $133.40  
  Purchase #3 $203.70   11.199%   $226.5124   $226.51   $226.50   $226.50  
  Purchase #4 $162.38   8.346%   $175.9322   $175.93   $175.95   $175.90  
  Purchase #5 $243.65   3.153%   $251.3323   $251.33   $251.35   $251.30  
  Purchase #6 $82.95   5.352%   $87.3895   $87.39   $87.40   $87.40  
  Purchase #7 $118.91   11.347%   $132.4027   $132.40   $132.40   $132.40  
  7 purchase totals = $1,172.20       $1,276.2059   $1,276.19   $1,276.25   $1,276.20