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	$52.67	10.319%	$58.105	$58.11	$58.10	$58.10
Purchase #2	$145.95	10.539%	$161.3317	$161.33	$161.35	$161.30
Purchase #3	$203.96	5.743%	$215.6734	$215.67	$215.65	$215.70
Purchase #4	$19.34	11.683%	$21.5995	$21.60	$21.60	$21.60
Purchase #5	$211.34	6.606%	$225.3011	$225.30	$225.30	$225.30
Purchase #6	$62.53	7.762%	$67.3836	$67.38	$67.40	$67.40
Purchase #7	$93.90	6.713%	$100.2035	$100.20	$100.20	$100.20
7 purchase totals =	$789.69		$849.5978	$849.59	$849.60	$849.60