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 $193.37   6.557%   $206.0493   $206.05   $206.05   $206.00  
  Purchase #2 $103.97   5.102%   $109.2745   $109.27   $109.25   $109.30  
  Purchase #3 $57.40   13.216%   $64.986   $64.99   $65.00   $65.00  
  Purchase #4 $196.67   10.145%   $216.6222   $216.62   $216.60   $216.60  
  Purchase #5 $47.25   13.564%   $53.659   $53.66   $53.65   $53.70  
  Purchase #6 $41.67   10.840%   $46.187   $46.19   $46.20   $46.20  
  Purchase #7 $204.51   8.164%   $221.2062   $221.21   $221.20   $221.20  
  7 purchase totals = $844.84       $917.9842   $917.99   $917.95   $918.00