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	$224.49	8.658%	$243.9263	$243.93	$243.95	$243.90
Purchase #2	$83.62	3.297%	$86.377	$86.38	$86.40	$86.40
Purchase #3	$85.90	4.713%	$89.9485	$89.95	$89.95	$89.90
Purchase #4	$153.46	4.503%	$160.3703	$160.37	$160.35	$160.40
Purchase #5	$22.31	10.511%	$24.655	$24.66	$24.65	$24.70
Purchase #6	$208.63	7.279%	$223.8162	$223.82	$223.80	$223.80
Purchase #7	$67.78	11.104%	$75.3063	$75.31	$75.30	$75.30
7 purchase totals =	$846.19		$904.3996	$904.42	$904.40	$904.40