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	$29.97	11.765%	$33.496	$33.50	$33.50	$33.50
Purchase #2	$39.48	3.663%	$40.9262	$40.93	$40.95	$40.90
Purchase #3	$156.30	9.548%	$171.2235	$171.22	$171.20	$171.20
Purchase #4	$209.39	3.814%	$217.3761	$217.38	$217.40	$217.40
Purchase #5	$88.89	11.716%	$99.3044	$99.30	$99.30	$99.30
Purchase #6	$33.42	11.377%	$37.2222	$37.22	$37.20	$37.20
Purchase #7	$246.84	3.133%	$254.5735	$254.57	$254.55	$254.60
7 purchase totals =	$804.29		$854.1219	$854.12	$854.10	$854.10