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	$247.31	13.812%	$281.4685	$281.47	$281.45	$281.50
Purchase #2	$60.95	10.187%	$67.159	$67.16	$67.15	$67.20
Purchase #3	$29.35	12.488%	$33.0152	$33.02	$33.00	$33.00
Purchase #4	$239.33	10.706%	$264.9527	$264.95	$264.95	$265.00
Purchase #5	$123.75	7.324%	$132.8135	$132.81	$132.80	$132.80
Purchase #6	$59.76	13.581%	$67.876	$67.88	$67.90	$67.90
Purchase #7	$81.41	5.432%	$85.8322	$85.83	$85.85	$85.80
7 purchase totals =	$841.86		$933.1171	$933.12	$933.10	$933.20