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	$116.93	3.375%	$120.8764	$120.88	$120.90	$120.90
Purchase #2	$243.47	7.476%	$261.6718	$261.67	$261.65	$261.70
Purchase #3	$193.32	6.450%	$205.7891	$205.79	$205.80	$205.80
Purchase #4	$30.88	8.528%	$33.5134	$33.51	$33.50	$33.50
Purchase #5	$38.37	5.287%	$40.3986	$40.40	$40.40	$40.40
Purchase #6	$209.86	13.516%	$238.2247	$238.22	$238.20	$238.20
Purchase #7	$179.35	5.609%	$189.4097	$189.41	$189.40	$189.40
7 purchase totals =	$1,012.18		$1,089.8837	$1,089.88	$1,089.85	$1,089.90