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	$172.29	8.439%	$186.8296	$186.83	$186.85	$186.80
Purchase #2	$179.97	9.296%	$196.7	$196.70	$196.70	$196.70
Purchase #3	$239.43	12.832%	$270.1537	$270.15	$270.15	$270.20
Purchase #4	$147.62	6.223%	$156.8064	$156.81	$156.80	$156.80
Purchase #5	$86.48	3.265%	$89.3036	$89.30	$89.30	$89.30
Purchase #6	$238.35	10.486%	$263.3434	$263.34	$263.35	$263.30
Purchase #7	$47.59	5.192%	$50.0609	$50.06	$50.05	$50.10
7 purchase totals =	$1,111.73		$1,213.1976	$1,213.19	$1,213.20	$1,213.20