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	$25.53	12.551%	$28.7343	$28.73	$28.75	$28.70
Purchase #2	$247.58	13.650%	$281.3747	$281.37	$281.35	$281.40
Purchase #3	$48.44	3.525%	$50.1475	$50.15	$50.15	$50.10
Purchase #4	$208.81	6.372%	$222.1154	$222.12	$222.10	$222.10
Purchase #5	$194.38	5.539%	$205.1467	$205.15	$205.15	$205.10
Purchase #6	$59.69	3.680%	$61.8866	$61.89	$61.90	$61.90
Purchase #7	$81.34	11.192%	$90.4436	$90.44	$90.45	$90.40
7 purchase totals =	$865.77		$939.8488	$939.85	$939.85	$939.70