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	$147.42	13.501%	$167.3232	$167.32	$167.30	$167.30
Purchase #2	$72.63	10.342%	$80.1414	$80.14	$80.15	$80.10
Purchase #3	$30.27	12.117%	$33.9378	$33.94	$33.95	$33.90
Purchase #4	$58.53	8.220%	$63.3412	$63.34	$63.35	$63.30
Purchase #5	$137.48	12.683%	$154.9166	$154.92	$154.90	$154.90
Purchase #6	$183.56	10.757%	$203.3055	$203.31	$203.30	$203.30
Purchase #7	$79.39	12.796%	$89.5487	$89.55	$89.55	$89.50
7 purchase totals =	$709.28		$792.5144	$792.52	$792.50	$792.30