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 $238.47   3.547%   $246.9285   $246.93   $246.95   $246.90  
  Purchase #2 $51.74   13.259%   $58.6002   $58.60   $58.60   $58.60  
  Purchase #3 $72.67   6.174%   $77.1566   $77.16   $77.15   $77.20  
  Purchase #4 $182.85   11.839%   $204.4976   $204.50   $204.50   $204.50  
  Purchase #5 $155.34   5.157%   $163.3509   $163.35   $163.35   $163.40  
  Purchase #6 $98.81   12.490%   $111.1514   $111.15   $111.15   $111.20  
  Purchase #7 $220.90   8.797%   $240.3326   $240.33   $240.35   $240.30  
  7 purchase totals = $1,020.78       $1,102.0178   $1,102.02   $1,102.05   $1,102.10