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	$201.30	10.374%	$222.1829	$222.18	$222.20	$222.20
Purchase #2	$114.54	9.225%	$125.1063	$125.11	$125.10	$125.10
Purchase #3	$61.35	10.274%	$67.6531	$67.65	$67.65	$67.70
Purchase #4	$47.43	8.634%	$51.5251	$51.53	$51.55	$51.50
Purchase #5	$79.30	12.696%	$89.3679	$89.37	$89.35	$89.40
Purchase #6	$86.75	12.774%	$97.8314	$97.83	$97.85	$97.80
Purchase #7	$123.94	9.640%	$135.8878	$135.89	$135.90	$135.90
7 purchase totals =	$714.61		$789.5545	$789.56	$789.60	$789.60