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 $208.77   8.624%   $226.7743   $226.77   $226.75   $226.80  
  Purchase #2 $44.71   11.309%   $49.7663   $49.77   $49.75   $49.80  
  Purchase #3 $228.88   10.794%   $253.5853   $253.59   $253.60   $253.60  
  Purchase #4 $16.62   3.777%   $17.2477   $17.25   $17.25   $17.20  
  Purchase #5 $191.85   5.862%   $203.0962   $203.10   $203.10   $203.10  
  Purchase #6 $7.42   7.440%   $7.972   $7.97   $7.95   $8.00  
  Purchase #7 $13.37   4.789%   $14.0103   $14.01   $14.00   $14.00  
  7 purchase totals = $711.62       $772.4521   $772.46   $772.40   $772.50