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	$141.25	12.720%	$159.217	$159.22	$159.20	$159.20
Purchase #2	$101.94	8.505%	$110.61	$110.61	$110.60	$110.60
Purchase #3	$236.33	13.505%	$268.2464	$268.25	$268.25	$268.20
Purchase #4	$52.69	12.112%	$59.0718	$59.07	$59.05	$59.10
Purchase #5	$145.64	11.847%	$162.894	$162.89	$162.90	$162.90
Purchase #6	$81.76	7.459%	$87.8585	$87.86	$87.85	$87.90
Purchase #7	$91.68	10.462%	$101.2716	$101.27	$101.25	$101.30
7 purchase totals =	$851.29		$949.1693	$949.17	$949.10	$949.20