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	$170.53	9.816%	$187.2692	$187.27	$187.25	$187.30
Purchase #2	$35.89	11.629%	$40.0636	$40.06	$40.05	$40.10
Purchase #3	$70.96	10.364%	$78.3143	$78.31	$78.30	$78.30
Purchase #4	$79.39	12.622%	$89.4106	$89.41	$89.40	$89.40
Purchase #5	$99.76	3.438%	$103.1897	$103.19	$103.20	$103.20
Purchase #6	$5.83	12.805%	$6.5765	$6.58	$6.60	$6.60
Purchase #7	$149.43	8.709%	$162.4439	$162.44	$162.45	$162.40
7 purchase totals =	$611.79		$667.2678	$667.26	$667.25	$667.30