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 $224.67   5.446%   $236.9055   $236.91   $236.90   $236.90  
  Purchase #2 $129.77   9.183%   $141.6868   $141.69   $141.70   $141.70  
  Purchase #3 $43.41   11.591%   $48.4417   $48.44   $48.45   $48.40  
  Purchase #4 $147.63   4.787%   $154.697   $154.70   $154.70   $154.70  
  Purchase #5 $186.76   9.124%   $203.8   $203.80   $203.80   $203.80  
  Purchase #6 $91.86   6.523%   $97.852   $97.85   $97.85   $97.90  
  Purchase #7 $249.65   7.452%   $268.2539   $268.25   $268.25   $268.30  
  7 purchase totals = $1,073.75       $1,151.6369   $1,151.64   $1,151.65   $1,151.70