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	$122.48	8.270%	$132.6091	$132.61	$132.60	$132.60
Purchase #2	$237.63	12.661%	$267.7163	$267.72	$267.70	$267.70
Purchase #3	$211.33	7.655%	$227.5073	$227.51	$227.50	$227.50
Purchase #4	$51.73	3.225%	$53.3983	$53.40	$53.40	$53.40
Purchase #5	$109.86	7.782%	$118.4093	$118.41	$118.40	$118.40
Purchase #6	$204.51	10.478%	$225.9386	$225.94	$225.95	$225.90
Purchase #7	$85.98	3.703%	$89.1638	$89.16	$89.15	$89.20
7 purchase totals =	$1,023.52		$1,114.7427	$1,114.75	$1,114.70	$1,114.70