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	$206.64	12.216%	$231.8831	$231.88	$231.90	$231.90
Purchase #2	$189.40	3.656%	$196.3245	$196.32	$196.30	$196.30
Purchase #3	$101.86	6.159%	$108.1336	$108.13	$108.15	$108.10
Purchase #4	$92.57	7.491%	$99.5044	$99.50	$99.50	$99.50
Purchase #5	$170.47	10.525%	$188.412	$188.41	$188.40	$188.40
Purchase #6	$118.54	5.543%	$125.1107	$125.11	$125.10	$125.10
Purchase #7	$101.33	8.496%	$109.939	$109.94	$109.95	$109.90
7 purchase totals =	$980.81		$1,059.3073	$1,059.29	$1,059.30	$1,059.20