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	$82.89	7.376%	$89.004	$89.00	$89.00	$89.00
Purchase #2	$45.89	13.347%	$52.0149	$52.01	$52.00	$52.00
Purchase #3	$245.90	10.144%	$270.8441	$270.84	$270.85	$270.80
Purchase #4	$246.48	13.305%	$279.2742	$279.27	$279.25	$279.30
Purchase #5	$203.48	6.301%	$216.3013	$216.30	$216.30	$216.30
Purchase #6	$125.55	8.447%	$136.1552	$136.16	$136.15	$136.20
Purchase #7	$26.59	10.318%	$29.3336	$29.33	$29.35	$29.30
7 purchase totals =	$976.78		$1,072.9273	$1,072.91	$1,072.90	$1,072.90