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	$75.65	10.285%	$83.4306	$83.43	$83.45	$83.40
Purchase #2	$29.44	12.738%	$33.1901	$33.19	$33.20	$33.20
Purchase #3	$81.83	8.483%	$88.7716	$88.77	$88.75	$88.80
Purchase #4	$42.29	6.811%	$45.1704	$45.17	$45.15	$45.20
Purchase #5	$151.38	10.443%	$167.1886	$167.19	$167.20	$167.20
Purchase #6	$89.85	7.468%	$96.56	$96.56	$96.55	$96.60
Purchase #7	$27.33	4.808%	$28.644	$28.64	$28.65	$28.60
7 purchase totals =	$497.77		$542.9553	$542.95	$542.95	$543.00