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 $59.91   10.247%   $66.049   $66.05   $66.05   $66.00  
  Purchase #2 $212.78   10.111%   $234.2942   $234.29   $234.30   $234.30  
  Purchase #3 $128.79   7.279%   $138.1646   $138.16   $138.15   $138.20  
  Purchase #4 $49.81   8.149%   $53.869   $53.87   $53.85   $53.90  
  Purchase #5 $142.51   10.312%   $157.2056   $157.21   $157.20   $157.20  
  Purchase #6 $194.28   6.197%   $206.3195   $206.32   $206.30   $206.30  
  Purchase #7 $12.49   10.560%   $13.8089   $13.81   $13.80   $13.80  
  7 purchase totals = $800.57       $869.7108   $869.71   $869.65   $869.70