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 $61.57   4.201%   $64.1566   $64.16   $64.15   $64.20  
  Purchase #2 $186.97   8.356%   $202.5932   $202.59   $202.60   $202.60  
  Purchase #3 $220.28   9.735%   $241.7243   $241.72   $241.70   $241.70  
  Purchase #4 $249.57   5.231%   $262.625   $262.63   $262.65   $262.60  
  Purchase #5 $107.35   6.314%   $114.1281   $114.13   $114.15   $114.10  
  Purchase #6 $240.86   9.384%   $263.4623   $263.46   $263.45   $263.50  
  Purchase #7 $242.94   10.658%   $268.8325   $268.83   $268.85   $268.80  
  7 purchase totals = $1,309.54       $1,417.5220   $1,417.52   $1,417.55   $1,417.50