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	$175.45	13.190%	$198.5919	$198.59	$198.60	$198.60
Purchase #2	$230.30	12.226%	$258.4565	$258.46	$258.45	$258.50
Purchase #3	$32.89	11.340%	$36.6197	$36.62	$36.60	$36.60
Purchase #4	$64.54	4.632%	$67.5295	$67.53	$67.55	$67.50
Purchase #5	$83.60	10.830%	$92.6539	$92.65	$92.65	$92.70
Purchase #6	$89.41	10.341%	$98.6559	$98.66	$98.65	$98.70
Purchase #7	$221.77	13.113%	$250.8507	$250.85	$250.85	$250.90
7 purchase totals =	$897.96		$1,003.3581	$1,003.36	$1,003.35	$1,003.50