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 $9.61   5.835%   $10.1707   $10.17   $10.15   $10.20  
  Purchase #2 $40.34   4.457%   $42.138   $42.14   $42.15   $42.10  
  Purchase #3 $164.29   9.774%   $180.3477   $180.35   $180.35   $180.30  
  Purchase #4 $240.85   11.172%   $267.7578   $267.76   $267.75   $267.80  
  Purchase #5 $147.73   8.254%   $159.9236   $159.92   $159.90   $159.90  
  Purchase #6 $158.58   7.240%   $170.0612   $170.06   $170.05   $170.10  
  Purchase #7 $243.38   10.532%   $269.0128   $269.01   $269.00   $269.00  
  7 purchase totals = $1,004.78       $1,099.4118   $1,099.41   $1,099.35   $1,099.40