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	$35.54	5.651%	$37.5484	$37.55	$37.55	$37.50
Purchase #2	$97.74	4.152%	$101.7982	$101.80	$101.80	$101.80
Purchase #3	$111.59	7.758%	$120.2472	$120.25	$120.25	$120.20
Purchase #4	$35.69	6.116%	$37.8728	$37.87	$37.85	$37.90
Purchase #5	$52.30	3.518%	$54.1399	$54.14	$54.15	$54.10
Purchase #6	$73.76	3.672%	$76.4685	$76.47	$76.45	$76.50
Purchase #7	$73.56	3.165%	$75.8882	$75.89	$75.90	$75.90
7 purchase totals =	$480.18		$503.9632	$503.97	$503.95	$503.90