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	$88.85	13.606%	$100.9389	$100.94	$100.95	$100.90
Purchase #2	$71.35	13.413%	$80.9202	$80.92	$80.90	$80.90
Purchase #3	$41.34	4.637%	$43.2569	$43.26	$43.25	$43.30
Purchase #4	$241.49	12.389%	$271.4082	$271.41	$271.40	$271.40
Purchase #5	$55.86	9.760%	$61.3119	$61.31	$61.30	$61.30
Purchase #6	$38.50	9.424%	$42.1282	$42.13	$42.15	$42.10
Purchase #7	$173.91	4.282%	$181.3568	$181.36	$181.35	$181.40
7 purchase totals =	$711.30		$781.3211	$781.33	$781.30	$781.30