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 $247.67   5.620%   $261.5891   $261.59   $261.60   $261.60  
  Purchase #2 $23.56   4.378%   $24.5915   $24.59   $24.60   $24.60  
  Purchase #3 $20.72   13.139%   $23.4424   $23.44   $23.45   $23.40  
  Purchase #4 $195.85   13.141%   $221.5866   $221.59   $221.60   $221.60  
  Purchase #5 $225.89   9.131%   $246.516   $246.52   $246.50   $246.50  
  Purchase #6 $19.72   3.102%   $20.3317   $20.33   $20.35   $20.30  
  Purchase #7 $36.48   8.487%   $39.5761   $39.58   $39.60   $39.60  
  7 purchase totals = $769.89       $837.6334   $837.64   $837.70   $837.60