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	$88.63	12.127%	$99.3782	$99.38	$99.40	$99.40
Purchase #2	$174.66	11.249%	$194.3075	$194.31	$194.30	$194.30
Purchase #3	$184.46	6.628%	$196.686	$196.69	$196.70	$196.70
Purchase #4	$65.48	9.596%	$71.7635	$71.76	$71.75	$71.80
Purchase #5	$134.28	10.811%	$148.797	$148.80	$148.80	$148.80
Purchase #6	$79.27	8.310%	$85.8573	$85.86	$85.85	$85.90
Purchase #7	$214.61	8.590%	$233.045	$233.05	$233.05	$233.00
7 purchase totals =	$941.39		$1,029.8345	$1,029.85	$1,029.85	$1,029.90