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 $206.94   13.711%   $235.3135   $235.31   $235.30   $235.30  
  Purchase #2 $162.69   12.710%   $183.3679   $183.37   $183.35   $183.40  
  Purchase #3 $223.50   11.515%   $249.236   $249.24   $249.25   $249.20  
  Purchase #4 $87.62   6.762%   $93.5449   $93.54   $93.55   $93.50  
  Purchase #5 $176.48   7.232%   $189.243   $189.24   $189.25   $189.20  
  Purchase #6 $181.30   8.492%   $196.696   $196.70   $196.70   $196.70  
  Purchase #7 $107.42   7.765%   $115.7612   $115.76   $115.75   $115.80  
  7 purchase totals = $1,145.95       $1,263.1625   $1,263.16   $1,263.15   $1,263.10