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 $125.54   13.613%   $142.6298   $142.63   $142.65   $142.60  
  Purchase #2 $243.40   11.647%   $271.7488   $271.75   $271.75   $271.70  
  Purchase #3 $23.66   13.390%   $26.8281   $26.83   $26.85   $26.80  
  Purchase #4 $126.84   6.386%   $134.94   $134.94   $134.95   $134.90  
  Purchase #5 $204.40   13.532%   $232.0594   $232.06   $232.05   $232.10  
  Purchase #6 $182.91   4.754%   $191.6055   $191.61   $191.60   $191.60  
  Purchase #7 $53.61   13.546%   $60.872   $60.87   $60.85   $60.90  
  7 purchase totals = $960.36       $1,060.6836   $1,060.69   $1,060.70   $1,060.60