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 $59.67   5.691%   $63.0658   $63.07   $63.05   $63.10  
  Purchase #2 $192.58   12.503%   $216.6583   $216.66   $216.65   $216.70  
  Purchase #3 $168.54   6.613%   $179.6856   $179.69   $179.70   $179.70  
  Purchase #4 $191.47   13.265%   $216.8685   $216.87   $216.85   $216.90  
  Purchase #5 $13.80   11.498%   $15.3867   $15.39   $15.40   $15.40  
  Purchase #6 $146.86   8.701%   $159.6383   $159.64   $159.65   $159.60  
  Purchase #7 $147.84   9.446%   $161.805   $161.81   $161.80   $161.80  
  7 purchase totals = $920.76       $1,013.1082   $1,013.13   $1,013.10   $1,013.20