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 $85.83   9.237%   $93.7581   $93.76   $93.75   $93.80  
  Purchase #2 $169.81   13.108%   $192.0687   $192.07   $192.05   $192.10  
  Purchase #3 $203.63   6.155%   $216.1634   $216.16   $216.15   $216.20  
  Purchase #4 $103.58   3.870%   $107.5885   $107.59   $107.60   $107.60  
  Purchase #5 $16.96   12.835%   $19.1368   $19.14   $19.15   $19.10  
  Purchase #6 $178.87   4.737%   $187.3431   $187.34   $187.35   $187.30  
  Purchase #7 $231.84   12.324%   $260.412   $260.41   $260.40   $260.40  
  7 purchase totals = $990.52       $1,076.4706   $1,076.47   $1,076.45   $1,076.50