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 $189.25   8.326%   $205.007   $205.01   $205.00   $205.00  
  Purchase #2 $68.59   8.817%   $74.6376   $74.64   $74.65   $74.60  
  Purchase #3 $142.72   9.844%   $156.7694   $156.77   $156.75   $156.80  
  Purchase #4 $176.44   10.724%   $195.3614   $195.36   $195.35   $195.40  
  Purchase #5 $202.53   8.379%   $219.5   $219.50   $219.50   $219.50  
  Purchase #6 $169.89   9.757%   $186.4662   $186.47   $186.45   $186.50  
  Purchase #7 $206.32   5.458%   $217.5809   $217.58   $217.60   $217.60  
  7 purchase totals = $1,155.74       $1,255.3225   $1,255.33   $1,255.30   $1,255.40