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 $141.98   11.562%   $158.3957   $158.40   $158.40   $158.40  
  Purchase #2 $237.62   6.557%   $253.2007   $253.20   $253.20   $253.20  
  Purchase #3 $107.94   9.626%   $118.3303   $118.33   $118.35   $118.30  
  Purchase #4 $140.74   10.662%   $155.7457   $155.75   $155.75   $155.70  
  Purchase #5 $188.30   9.467%   $206.1264   $206.13   $206.15   $206.10  
  Purchase #6 $241.36   3.368%   $249.489   $249.49   $249.50   $249.50  
  Purchase #7 $113.27   12.367%   $127.2781   $127.28   $127.30   $127.30  
  7 purchase totals = $1,171.21       $1,268.5659   $1,268.58   $1,268.65   $1,268.50