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	$240.49	4.241%	$250.6892	$250.69	$250.70	$250.70
Purchase #2	$173.50	13.290%	$196.5582	$196.56	$196.55	$196.60
Purchase #3	$59.48	9.745%	$65.2763	$65.28	$65.30	$65.30
Purchase #4	$46.46	12.276%	$52.1634	$52.16	$52.15	$52.20
Purchase #5	$25.94	9.503%	$28.4051	$28.41	$28.40	$28.40
Purchase #6	$175.40	7.863%	$189.1917	$189.19	$189.20	$189.20
Purchase #7	$6.82	12.274%	$7.6571	$7.66	$7.65	$7.70
7 purchase totals =	$728.09		$789.9410	$789.95	$789.95	$790.10