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 $240.54   9.815%   $264.149   $264.15   $264.15   $264.10  
  Purchase #2 $187.28   3.467%   $193.773   $193.77   $193.75   $193.80  
  Purchase #3 $56.56   12.436%   $63.5938   $63.59   $63.60   $63.60  
  Purchase #4 $106.95   11.181%   $118.9081   $118.91   $118.90   $118.90  
  Purchase #5 $18.91   4.754%   $19.809   $19.81   $19.80   $19.80  
  Purchase #6 $250.53   10.221%   $276.1367   $276.14   $276.15   $276.10  
  Purchase #7 $122.47   10.543%   $135.382   $135.38   $135.40   $135.40  
  7 purchase totals = $983.24       $1,071.7516   $1,071.75   $1,071.75   $1,071.70