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	$115.57	12.575%	$130.1029	$130.10	$130.10	$130.10
Purchase #2	$247.43	8.157%	$267.6129	$267.61	$267.60	$267.60
Purchase #3	$73.52	11.851%	$82.2329	$82.23	$82.25	$82.20
Purchase #4	$41.64	6.842%	$44.489	$44.49	$44.50	$44.50
Purchase #5	$189.95	3.666%	$196.9136	$196.91	$196.90	$196.90
Purchase #6	$159.59	6.233%	$169.5372	$169.54	$169.55	$169.50
Purchase #7	$94.81	11.553%	$105.7634	$105.76	$105.75	$105.80
7 purchase totals =	$922.51		$996.6519	$996.64	$996.65	$996.60