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 $95.58   4.211%   $99.6049   $99.60   $99.60   $99.60  
  Purchase #2 $191.48   10.176%   $210.965   $210.97   $210.95   $211.00  
  Purchase #3 $230.92   11.223%   $256.8362   $256.84   $256.85   $256.80  
  Purchase #4 $196.49   8.788%   $213.7575   $213.76   $213.75   $213.80  
  Purchase #5 $177.47   3.769%   $184.1588   $184.16   $184.15   $184.20  
  Purchase #6 $158.75   10.439%   $175.3219   $175.32   $175.30   $175.30  
  Purchase #7 $77.91   13.362%   $88.3203   $88.32   $88.30   $88.30  
  7 purchase totals = $1,128.60       $1,228.9646   $1,228.97   $1,228.90   $1,229.00