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 $225.71   9.554%   $247.2743   $247.27   $247.25   $247.30  
  Purchase #2 $77.92   12.250%   $87.4652   $87.47   $87.45   $87.50  
  Purchase #3 $187.33   6.113%   $198.7815   $198.78   $198.80   $198.80  
  Purchase #4 $224.59   5.490%   $236.92   $236.92   $236.90   $236.90  
  Purchase #5 $237.78   10.831%   $263.534   $263.53   $263.55   $263.50  
  Purchase #6 $87.84   7.293%   $94.2462   $94.25   $94.25   $94.20  
  Purchase #7 $77.36   3.832%   $80.3244   $80.32   $80.30   $80.30  
  7 purchase totals = $1,118.53       $1,208.5456   $1,208.54   $1,208.50   $1,208.50