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 $245.55   9.527%   $268.9435   $268.94   $268.95   $268.90  
  Purchase #2 $68.82   7.538%   $74.0077   $74.01   $74.00   $74.00  
  Purchase #3 $241.61   6.222%   $256.643   $256.64   $256.65   $256.60  
  Purchase #4 $248.37   13.861%   $282.7966   $282.80   $282.80   $282.80  
  Purchase #5 $10.82   9.468%   $11.8444   $11.84   $11.85   $11.80  
  Purchase #6 $218.48   11.682%   $244.0028   $244.00   $244.00   $244.00  
  Purchase #7 $169.87   12.874%   $191.7391   $191.74   $191.75   $191.70  
  7 purchase totals = $1,203.52       $1,329.9771   $1,329.97   $1,330.00   $1,329.80