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 $76.64   10.481%   $84.6726   $84.67   $84.65   $84.70  
  Purchase #2 $45.97   12.535%   $51.7323   $51.73   $51.75   $51.70  
  Purchase #3 $217.51   11.109%   $241.6732   $241.67   $241.65   $241.70  
  Purchase #4 $20.83   9.782%   $22.8676   $22.87   $22.85   $22.90  
  Purchase #5 $134.90   5.266%   $142.0038   $142.00   $142.00   $142.00  
  Purchase #6 $12.79   13.625%   $14.5326   $14.53   $14.55   $14.50  
  Purchase #7 $123.34   10.592%   $136.4042   $136.40   $136.40   $136.40  
  7 purchase totals = $631.98       $693.8863   $693.87   $693.85   $693.90