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 $59.38   11.544%   $66.2348   $66.23   $66.25   $66.20  
  Purchase #2 $139.51   9.645%   $152.9657   $152.97   $152.95   $153.00  
  Purchase #3 $187.57   8.823%   $204.1193   $204.12   $204.10   $204.10  
  Purchase #4 $92.75   6.231%   $98.5293   $98.53   $98.55   $98.50  
  Purchase #5 $63.29   11.291%   $70.4361   $70.44   $70.45   $70.40  
  Purchase #6 $216.71   4.688%   $226.8694   $226.87   $226.85   $226.90  
  Purchase #7 $249.92   8.874%   $272.0979   $272.10   $272.10   $272.10  
  7 purchase totals = $1,009.13       $1,091.2525   $1,091.26   $1,091.25   $1,091.20