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 $114.57   4.326%   $119.5263   $119.53   $119.55   $119.50  
  Purchase #2 $195.61   10.784%   $216.7046   $216.70   $216.70   $216.70  
  Purchase #3 $122.84   4.202%   $128.0017   $128.00   $128.00   $128.00  
  Purchase #4 $149.82   8.209%   $162.1187   $162.12   $162.10   $162.10  
  Purchase #5 $154.54   11.423%   $172.1931   $172.19   $172.20   $172.20  
  Purchase #6 $50.93   6.348%   $54.163   $54.16   $54.15   $54.20  
  Purchase #7 $155.98   8.340%   $168.9887   $168.99   $169.00   $169.00  
  7 purchase totals = $944.29       $1,021.6961   $1,021.69   $1,021.70   $1,021.70