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 $233.94   8.871%   $254.6928   $254.69   $254.70   $254.70  
  Purchase #2 $181.61   13.169%   $205.5262   $205.53   $205.55   $205.50  
  Purchase #3 $77.95   9.511%   $85.3638   $85.36   $85.35   $85.40  
  Purchase #4 $13.68   12.690%   $15.416   $15.42   $15.40   $15.40  
  Purchase #5 $213.57   13.392%   $242.1713   $242.17   $242.15   $242.20  
  Purchase #6 $179.65   4.659%   $188.0199   $188.02   $188.00   $188.00  
  Purchase #7 $191.33   12.265%   $214.7966   $214.80   $214.80   $214.80  
  7 purchase totals = $1,091.73       $1,205.9866   $1,205.99   $1,205.95   $1,206.00