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 $151.59   8.570%   $164.5813   $164.58   $164.60   $164.60  
  Purchase #2 $49.26   10.295%   $54.3313   $54.33   $54.35   $54.30  
  Purchase #3 $23.50   13.457%   $26.6624   $26.66   $26.65   $26.70  
  Purchase #4 $203.76   8.428%   $220.9329   $220.93   $220.95   $220.90  
  Purchase #5 $246.35   10.255%   $271.6132   $271.61   $271.60   $271.60  
  Purchase #6 $86.41   13.434%   $98.0183   $98.02   $98.00   $98.00  
  Purchase #7 $247.30   12.519%   $278.2595   $278.26   $278.25   $278.30  
  7 purchase totals = $1,008.17       $1,114.3989   $1,114.39   $1,114.40   $1,114.40