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	$115.96	3.407%	$119.9108	$119.91	$119.90	$119.90
Purchase #2	$216.48	3.605%	$224.2841	$224.28	$224.30	$224.30
Purchase #3	$67.66	8.293%	$73.271	$73.27	$73.25	$73.30
Purchase #4	$137.91	5.613%	$145.6509	$145.65	$145.65	$145.70
Purchase #5	$32.46	3.430%	$33.5734	$33.57	$33.55	$33.60
Purchase #6	$181.68	8.402%	$196.9448	$196.94	$196.95	$196.90
Purchase #7	$19.61	3.377%	$20.2722	$20.27	$20.25	$20.30
7 purchase totals =	$771.76		$813.9072	$813.89	$813.85	$814.00