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	$88.87	11.864%	$99.4135	$99.41	$99.40	$99.40
Purchase #2	$49.91	4.315%	$52.0636	$52.06	$52.05	$52.10
Purchase #3	$202.49	11.167%	$225.1021	$225.10	$225.10	$225.10
Purchase #4	$246.63	6.280%	$262.1184	$262.12	$262.10	$262.10
Purchase #5	$188.36	8.495%	$204.3612	$204.36	$204.35	$204.40
Purchase #6	$85.71	13.562%	$97.334	$97.33	$97.35	$97.30
Purchase #7	$152.66	4.761%	$159.9281	$159.93	$159.95	$159.90
7 purchase totals =	$1,014.63		$1,100.3209	$1,100.31	$1,100.30	$1,100.30