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 $86.58   13.865%   $98.5843   $98.58   $98.60   $98.60  
  Purchase #2 $54.34   13.431%   $61.6384   $61.64   $61.65   $61.60  
  Purchase #3 $237.26   9.648%   $260.1508   $260.15   $260.15   $260.20  
  Purchase #4 $248.58   6.197%   $263.9845   $263.98   $264.00   $264.00  
  Purchase #5 $56.29   5.402%   $59.3308   $59.33   $59.35   $59.30  
  Purchase #6 $221.27   3.694%   $229.4437   $229.44   $229.45   $229.40  
  Purchase #7 $155.78   3.745%   $161.614   $161.61   $161.60   $161.60  
  7 purchase totals = $1,060.10       $1,134.7465   $1,134.73   $1,134.80   $1,134.70