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	$140.69	12.414%	$158.1553	$158.16	$158.15	$158.20
Purchase #2	$222.41	12.208%	$249.5618	$249.56	$249.55	$249.60
Purchase #3	$152.99	7.825%	$164.9615	$164.96	$164.95	$165.00
Purchase #4	$170.43	12.323%	$191.4321	$191.43	$191.45	$191.40
Purchase #5	$120.31	7.419%	$129.2358	$129.24	$129.25	$129.20
Purchase #6	$49.90	7.868%	$53.8261	$53.83	$53.85	$53.80
Purchase #7	$78.27	5.615%	$82.6649	$82.66	$82.65	$82.70
7 purchase totals =	$935.00		$1,029.8375	$1,029.84	$1,029.85	$1,029.90