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 $80.98   8.177%   $87.6017   $87.60   $87.60   $87.60  
  Purchase #2 $61.92   8.122%   $66.9491   $66.95   $66.95   $66.90  
  Purchase #3 $206.46   5.245%   $217.2888   $217.29   $217.30   $217.30  
  Purchase #4 $219.67   13.134%   $248.5215   $248.52   $248.50   $248.50  
  Purchase #5 $133.35   10.261%   $147.033   $147.03   $147.05   $147.00  
  Purchase #6 $233.27   13.129%   $263.896   $263.90   $263.90   $263.90  
  Purchase #7 $79.55   8.287%   $86.1423   $86.14   $86.15   $86.10  
  7 purchase totals = $1,015.20       $1,117.4324   $1,117.43   $1,117.45   $1,117.30