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	$31.50	12.503%	$35.4384	$35.44	$35.45	$35.40
Purchase #2	$74.55	10.178%	$82.1377	$82.14	$82.15	$82.10
Purchase #3	$54.84	4.832%	$57.4899	$57.49	$57.50	$57.50
Purchase #4	$214.73	3.543%	$222.3379	$222.34	$222.35	$222.30
Purchase #5	$164.31	13.489%	$186.4738	$186.47	$186.45	$186.50
Purchase #6	$147.79	8.869%	$160.8975	$160.90	$160.90	$160.90
Purchase #7	$240.81	7.539%	$258.9647	$258.96	$258.95	$259.00
7 purchase totals =	$928.53		$1,003.7399	$1,003.74	$1,003.75	$1,003.70