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	$51.43	12.267%	$57.7389	$57.74	$57.75	$57.70
Purchase #2	$209.30	6.716%	$223.3566	$223.36	$223.35	$223.40
Purchase #3	$99.66	4.853%	$104.4965	$104.50	$104.50	$104.50
Purchase #4	$196.67	13.645%	$223.5056	$223.51	$223.50	$223.50
Purchase #5	$129.42	12.271%	$145.3011	$145.30	$145.30	$145.30
Purchase #6	$139.29	8.372%	$150.9514	$150.95	$150.95	$151.00
Purchase #7	$139.53	11.483%	$155.5522	$155.55	$155.55	$155.60
7 purchase totals =	$965.30		$1,060.9023	$1,060.91	$1,060.90	$1,061.00