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 $155.42   10.120%   $171.1485   $171.15   $171.15   $171.10  
  Purchase #2 $19.81   13.581%   $22.5004   $22.50   $22.50   $22.50  
  Purchase #3 $160.45   5.622%   $169.4705   $169.47   $169.45   $169.50  
  Purchase #4 $190.45   13.572%   $216.2979   $216.30   $216.30   $216.30  
  Purchase #5 $53.57   12.699%   $60.3729   $60.37   $60.35   $60.40  
  Purchase #6 $239.73   7.201%   $256.993   $256.99   $257.00   $257.00  
  Purchase #7 $242.98   9.181%   $265.288   $265.29   $265.30   $265.30  
  7 purchase totals = $1,062.41       $1,162.0712   $1,162.07   $1,162.05   $1,162.10