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	$235.83	12.154%	$264.4928	$264.49	$264.50	$264.50
Purchase #2	$51.76	6.279%	$55.01	$55.01	$55.00	$55.00
Purchase #3	$142.46	3.846%	$147.939	$147.94	$147.95	$147.90
Purchase #4	$217.29	12.165%	$243.7233	$243.72	$243.70	$243.70
Purchase #5	$185.29	6.103%	$196.5982	$196.60	$196.60	$196.60
Purchase #6	$121.36	11.668%	$135.5203	$135.52	$135.50	$135.50
Purchase #7	$43.44	13.186%	$49.168	$49.17	$49.15	$49.20
7 purchase totals =	$997.43		$1,092.4516	$1,092.45	$1,092.40	$1,092.40