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	$235.79	4.478%	$246.3487	$246.35	$246.35	$246.30
Purchase #2	$124.50	13.492%	$141.2975	$141.30	$141.30	$141.30
Purchase #3	$181.79	8.185%	$196.6695	$196.67	$196.65	$196.70
Purchase #4	$189.58	4.295%	$197.7225	$197.72	$197.70	$197.70
Purchase #5	$115.88	10.376%	$127.9037	$127.90	$127.90	$127.90
Purchase #6	$137.84	9.199%	$150.5199	$150.52	$150.50	$150.50
Purchase #7	$244.48	13.516%	$277.5239	$277.52	$277.50	$277.50
7 purchase totals =	$1,229.86		$1,337.9857	$1,337.98	$1,337.90	$1,337.90