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 $34.57   3.452%   $35.7634   $35.76   $35.75   $35.80  
  Purchase #2 $133.91   10.306%   $147.7108   $147.71   $147.70   $147.70  
  Purchase #3 $201.42   8.590%   $218.722   $218.72   $218.70   $218.70  
  Purchase #4 $108.42   3.856%   $112.6007   $112.60   $112.60   $112.60  
  Purchase #5 $187.52   7.355%   $201.3121   $201.31   $201.30   $201.30  
  Purchase #6 $236.96   5.483%   $249.9525   $249.95   $249.95   $250.00  
  Purchase #7 $45.26   7.366%   $48.5939   $48.59   $48.60   $48.60  
  7 purchase totals = $948.06       $1,014.6554   $1,014.64   $1,014.60   $1,014.70