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 $215.85   12.424%   $242.6672   $242.67   $242.65   $242.70  
  Purchase #2 $187.33   9.433%   $205.0008   $205.00   $205.00   $205.00  
  Purchase #3 $178.99   3.434%   $185.1365   $185.14   $185.15   $185.10  
  Purchase #4 $60.62   3.260%   $62.5962   $62.60   $62.60   $62.60  
  Purchase #5 $243.92   8.349%   $264.2849   $264.28   $264.30   $264.30  
  Purchase #6 $40.28   7.217%   $43.187   $43.19   $43.20   $43.20  
  Purchase #7 $56.63   13.223%   $64.1182   $64.12   $64.10   $64.10  
  7 purchase totals = $983.62       $1,066.9908   $1,067.00   $1,067.00   $1,067.00