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	$220.70	4.180%	$229.9253	$229.93	$229.95	$229.90
Purchase #2	$234.50	12.705%	$264.2932	$264.29	$264.30	$264.30
Purchase #3	$135.33	6.764%	$144.4837	$144.48	$144.50	$144.50
Purchase #4	$223.34	8.289%	$241.8527	$241.85	$241.85	$241.90
Purchase #5	$7.84	8.178%	$8.4812	$8.48	$8.50	$8.50
Purchase #6	$156.65	11.306%	$174.3608	$174.36	$174.35	$174.40
Purchase #7	$40.28	3.667%	$41.7571	$41.76	$41.75	$41.80
7 purchase totals =	$1,018.64		$1,105.1540	$1,105.15	$1,105.20	$1,105.30