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 $98.58   7.829%   $106.2978   $106.30   $106.30   $106.30  
  Purchase #2 $246.57   9.301%   $269.5035   $269.50   $269.50   $269.50  
  Purchase #3 $246.80   3.717%   $255.9736   $255.97   $255.95   $256.00  
  Purchase #4 $69.59   5.269%   $73.2567   $73.26   $73.25   $73.30  
  Purchase #5 $207.63   8.819%   $225.9409   $225.94   $225.95   $225.90  
  Purchase #6 $200.71   6.223%   $213.2002   $213.20   $213.20   $213.20  
  Purchase #7 $5.87   3.386%   $6.0688   $6.07   $6.05   $6.10  
  7 purchase totals = $1,075.75       $1,150.2415   $1,150.24   $1,150.20   $1,150.30