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	$223.57	13.377%	$253.477	$253.48	$253.50	$253.50
Purchase #2	$110.91	11.201%	$123.333	$123.33	$123.35	$123.30
Purchase #3	$18.71	12.654%	$21.0776	$21.08	$21.10	$21.10
Purchase #4	$226.31	4.429%	$236.3333	$236.33	$236.35	$236.30
Purchase #5	$62.59	13.281%	$70.9026	$70.90	$70.90	$70.90
Purchase #6	$70.40	11.334%	$78.3791	$78.38	$78.40	$78.40
Purchase #7	$55.91	10.375%	$61.7107	$61.71	$61.70	$61.70
7 purchase totals =	$768.40		$845.2133	$845.21	$845.30	$845.20