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	$84.56	11.486%	$94.2726	$94.27	$94.25	$94.30
Purchase #2	$40.25	10.684%	$44.5503	$44.55	$44.55	$44.60
Purchase #3	$167.68	10.799%	$185.7878	$185.79	$185.80	$185.80
Purchase #4	$72.36	8.202%	$78.295	$78.30	$78.30	$78.30
Purchase #5	$36.33	9.181%	$39.6655	$39.67	$39.65	$39.70
Purchase #6	$143.43	11.809%	$160.3676	$160.37	$160.35	$160.40
Purchase #7	$181.29	8.603%	$196.8864	$196.89	$196.90	$196.90
7 purchase totals =	$725.90		$799.8252	$799.84	$799.80	$800.00