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 $233.67   5.493%   $246.5055   $246.51   $246.50   $246.50  
  Purchase #2 $22.49   5.371%   $23.6979   $23.70   $23.70   $23.70  
  Purchase #3 $36.26   7.786%   $39.0832   $39.08   $39.10   $39.10  
  Purchase #4 $241.85   3.248%   $249.7053   $249.71   $249.70   $249.70  
  Purchase #5 $123.91   6.407%   $131.8489   $131.85   $131.85   $131.80  
  Purchase #6 $95.87   5.673%   $101.3087   $101.31   $101.30   $101.30  
  Purchase #7 $62.50   5.144%   $65.715   $65.72   $65.70   $65.70  
  7 purchase totals = $816.55       $857.8645   $857.88   $857.85   $857.80