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 $114.53   6.779%   $122.294   $122.29   $122.30   $122.30  
  Purchase #2 $168.51   10.789%   $186.6905   $186.69   $186.70   $186.70  
  Purchase #3 $184.56   12.536%   $207.6964   $207.70   $207.70   $207.70  
  Purchase #4 $197.85   10.232%   $218.094   $218.09   $218.10   $218.10  
  Purchase #5 $204.50   5.594%   $215.9397   $215.94   $215.95   $215.90  
  Purchase #6 $167.93   10.429%   $185.4434   $185.44   $185.45   $185.40  
  Purchase #7 $187.55   12.528%   $211.0463   $211.05   $211.05   $211.00  
  7 purchase totals = $1,225.43       $1,347.2043   $1,347.20   $1,347.25   $1,347.10