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	$75.94	4.340%	$79.2358	$79.24	$79.25	$79.20
Purchase #2	$64.78	11.601%	$72.2951	$72.30	$72.30	$72.30
Purchase #3	$37.75	12.681%	$42.5371	$42.54	$42.55	$42.50
Purchase #4	$236.69	3.242%	$244.3635	$244.36	$244.35	$244.40
Purchase #5	$59.34	12.498%	$66.7563	$66.76	$66.75	$66.80
Purchase #6	$115.58	7.383%	$124.1133	$124.11	$124.10	$124.10
Purchase #7	$152.35	9.640%	$167.0365	$167.04	$167.05	$167.00
7 purchase totals =	$742.43		$796.3376	$796.35	$796.35	$796.30