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 $243.67   4.479%   $254.584   $254.58   $254.60   $254.60  
  Purchase #2 $135.33   9.812%   $148.6086   $148.61   $148.60   $148.60  
  Purchase #3 $119.66   7.852%   $129.0557   $129.06   $129.05   $129.10  
  Purchase #4 $18.51   12.753%   $20.8706   $20.87   $20.85   $20.90  
  Purchase #5 $72.57   11.591%   $80.9816   $80.98   $81.00   $81.00  
  Purchase #6 $206.43   7.239%   $221.3735   $221.37   $221.35   $221.40  
  Purchase #7 $207.90   8.670%   $225.9249   $225.92   $225.90   $225.90  
  7 purchase totals = $1,004.07       $1,081.3989   $1,081.39   $1,081.35   $1,081.50