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 $173.46   11.842%   $194.0011   $194.00   $194.00   $194.00  
  Purchase #2 $67.74   5.701%   $71.6019   $71.60   $71.60   $71.60  
  Purchase #3 $42.46   7.141%   $45.4921   $45.49   $45.50   $45.50  
  Purchase #4 $113.48   3.173%   $117.0807   $117.08   $117.10   $117.10  
  Purchase #5 $72.70   4.532%   $75.9948   $75.99   $76.00   $76.00  
  Purchase #6 $88.47   5.423%   $93.2677   $93.27   $93.25   $93.30  
  Purchase #7 $133.48   13.604%   $151.6386   $151.64   $151.65   $151.60  
  7 purchase totals = $691.79       $749.0769   $749.07   $749.10   $749.10