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	$170.59	8.569%	$185.2079	$185.21	$185.20	$185.20
Purchase #2	$61.38	9.846%	$67.4235	$67.42	$67.40	$67.40
Purchase #3	$45.82	10.790%	$50.764	$50.76	$50.75	$50.80
Purchase #4	$165.31	12.732%	$186.3573	$186.36	$186.35	$186.40
Purchase #5	$35.81	6.287%	$38.0614	$38.06	$38.05	$38.10
Purchase #6	$62.56	13.316%	$70.8905	$70.89	$70.90	$70.90
Purchase #7	$165.69	6.173%	$175.918	$175.92	$175.90	$175.90
7 purchase totals =	$707.16		$774.6226	$774.62	$774.55	$774.70