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	$76.46	12.720%	$86.1857	$86.19	$86.20	$86.20
Purchase #2	$209.36	6.720%	$223.429	$223.43	$223.45	$223.40
Purchase #3	$42.36	9.240%	$46.2741	$46.27	$46.25	$46.30
Purchase #4	$151.47	8.351%	$164.1193	$164.12	$164.10	$164.10
Purchase #5	$59.26	13.674%	$67.3632	$67.36	$67.35	$67.40
Purchase #6	$85.31	3.199%	$88.0391	$88.04	$88.05	$88.00
Purchase #7	$188.88	12.157%	$211.8421	$211.84	$211.85	$211.80
7 purchase totals =	$813.10		$887.2525	$887.25	$887.25	$887.20