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	$218.41	11.674%	$243.9072	$243.91	$243.90	$243.90
Purchase #2	$183.60	3.104%	$189.2989	$189.30	$189.30	$189.30
Purchase #3	$88.79	10.874%	$98.445	$98.45	$98.45	$98.40
Purchase #4	$79.29	12.282%	$89.0284	$89.03	$89.05	$89.00
Purchase #5	$19.31	5.592%	$20.3898	$20.39	$20.40	$20.40
Purchase #6	$229.53	10.231%	$253.0132	$253.01	$253.00	$253.00
Purchase #7	$166.47	13.648%	$189.1898	$189.19	$189.20	$189.20
7 purchase totals =	$985.40		$1,083.2723	$1,083.28	$1,083.30	$1,083.20