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	$83.31	12.220%	$93.4905	$93.49	$93.50	$93.50
Purchase #2	$116.66	11.456%	$130.0246	$130.02	$130.00	$130.00
Purchase #3	$116.61	6.583%	$124.2864	$124.29	$124.30	$124.30
Purchase #4	$42.25	7.560%	$45.4441	$45.44	$45.45	$45.40
Purchase #5	$144.51	11.196%	$160.6893	$160.69	$160.70	$160.70
Purchase #6	$49.61	10.689%	$54.9128	$54.91	$54.90	$54.90
Purchase #7	$215.91	11.279%	$240.2625	$240.26	$240.25	$240.30
7 purchase totals =	$768.86		$849.1102	$849.10	$849.10	$849.10