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 $149.65   12.830%   $168.8501   $168.85   $168.85   $168.90  
  Purchase #2 $109.27   9.389%   $119.5294   $119.53   $119.55   $119.50  
  Purchase #3 $176.65   3.801%   $183.3645   $183.36   $183.35   $183.40  
  Purchase #4 $246.30   3.726%   $255.4771   $255.48   $255.50   $255.50  
  Purchase #5 $86.93   8.729%   $94.5181   $94.52   $94.50   $94.50  
  Purchase #6 $178.60   8.133%   $193.1255   $193.13   $193.15   $193.10  
  Purchase #7 $7.64   11.557%   $8.523   $8.52   $8.50   $8.50  
  7 purchase totals = $955.04       $1,023.3877   $1,023.39   $1,023.40   $1,023.40