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	$19.53	7.471%	$20.9891	$20.99	$21.00	$21.00
Purchase #2	$245.31	7.769%	$264.3681	$264.37	$264.35	$264.40
Purchase #3	$111.51	6.159%	$118.3779	$118.38	$118.40	$118.40
Purchase #4	$136.61	10.186%	$150.5251	$150.53	$150.55	$150.50
Purchase #5	$93.70	8.173%	$101.3581	$101.36	$101.35	$101.40
Purchase #6	$127.50	11.274%	$141.8744	$141.87	$141.85	$141.90
Purchase #7	$194.73	9.335%	$212.908	$212.91	$212.90	$212.90
7 purchase totals =	$928.89		$1,010.4007	$1,010.41	$1,010.40	$1,010.50