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	$23.28	12.419%	$26.1711	$26.17	$26.15	$26.20
Purchase #2	$214.70	4.801%	$225.0077	$225.01	$225.00	$225.00
Purchase #3	$128.47	8.471%	$139.3527	$139.35	$139.35	$139.40
Purchase #4	$168.61	6.598%	$179.7349	$179.73	$179.75	$179.70
Purchase #5	$83.27	7.150%	$89.2238	$89.22	$89.20	$89.20
Purchase #6	$25.41	11.501%	$28.3324	$28.33	$28.35	$28.30
Purchase #7	$77.38	6.653%	$82.5281	$82.53	$82.55	$82.50
7 purchase totals =	$721.12		$770.3507	$770.34	$770.35	$770.30