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 $240.90   8.776%   $262.0414   $262.04   $262.05   $262.00  
  Purchase #2 $21.51   6.135%   $22.8296   $22.83   $22.85   $22.80  
  Purchase #3 $65.55   13.744%   $74.5592   $74.56   $74.55   $74.60  
  Purchase #4 $63.85   6.211%   $67.8157   $67.82   $67.80   $67.80  
  Purchase #5 $187.71   12.774%   $211.6881   $211.69   $211.70   $211.70  
  Purchase #6 $236.67   9.779%   $259.814   $259.81   $259.80   $259.80  
  Purchase #7 $44.76   4.810%   $46.913   $46.91   $46.90   $46.90  
  7 purchase totals = $860.95       $945.6610   $945.66   $945.65   $945.60