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	$245.40	12.818%	$276.8554	$276.86	$276.85	$276.90
Purchase #2	$31.58	13.675%	$35.8986	$35.90	$35.90	$35.90
Purchase #3	$37.47	12.862%	$42.2894	$42.29	$42.30	$42.30
Purchase #4	$178.35	4.138%	$185.7301	$185.73	$185.75	$185.70
Purchase #5	$223.95	4.160%	$233.2663	$233.27	$233.25	$233.30
Purchase #6	$37.46	12.741%	$42.2328	$42.23	$42.25	$42.20
Purchase #7	$100.66	4.579%	$105.2692	$105.27	$105.25	$105.30
7 purchase totals =	$854.87		$921.5418	$921.55	$921.55	$921.60