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	$127.27	3.198%	$131.3401	$131.34	$131.35	$131.30
Purchase #2	$195.65	6.471%	$208.3105	$208.31	$208.30	$208.30
Purchase #3	$24.43	12.745%	$27.5436	$27.54	$27.55	$27.50
Purchase #4	$78.51	6.830%	$83.8722	$83.87	$83.85	$83.90
Purchase #5	$231.60	6.107%	$245.7438	$245.74	$245.75	$245.70
Purchase #6	$210.73	10.705%	$233.2886	$233.29	$233.30	$233.30
Purchase #7	$158.85	12.464%	$178.6491	$178.65	$178.65	$178.60
7 purchase totals =	$1,027.04		$1,108.7479	$1,108.74	$1,108.75	$1,108.60