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 $117.96   8.608%   $128.114   $128.11   $128.10   $128.10  
  Purchase #2 $233.61   3.871%   $242.653   $242.65   $242.65   $242.70  
  Purchase #3 $227.54   11.619%   $253.9779   $253.98   $254.00   $254.00  
  Purchase #4 $217.46   5.696%   $229.8465   $229.85   $229.85   $229.80  
  Purchase #5 $34.52   5.333%   $36.361   $36.36   $36.35   $36.40  
  Purchase #6 $248.59   6.726%   $265.3102   $265.31   $265.30   $265.30  
  Purchase #7 $87.85   12.421%   $98.7618   $98.76   $98.75   $98.80  
  7 purchase totals = $1,167.53       $1,255.0244   $1,255.02   $1,255.00   $1,255.10