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 $186.99   10.831%   $207.2429   $207.24   $207.25   $207.20  
  Purchase #2 $75.52   3.193%   $77.9314   $77.93   $77.95   $77.90  
  Purchase #3 $23.95   4.125%   $24.9379   $24.94   $24.95   $24.90  
  Purchase #4 $87.81   4.736%   $91.9687   $91.97   $91.95   $92.00  
  Purchase #5 $176.51   10.233%   $194.5723   $194.57   $194.55   $194.60  
  Purchase #6 $74.33   10.603%   $82.2112   $82.21   $82.20   $82.20  
  Purchase #7 $77.89   7.176%   $83.4794   $83.48   $83.50   $83.50  
  7 purchase totals = $703.00       $762.3438   $762.34   $762.35   $762.30