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	$145.94	4.510%	$152.5219	$152.52	$152.50	$152.50
Purchase #2	$157.63	10.677%	$174.4602	$174.46	$174.45	$174.50
Purchase #3	$72.44	10.336%	$79.9274	$79.93	$79.95	$79.90
Purchase #4	$215.84	7.240%	$231.4668	$231.47	$231.45	$231.50
Purchase #5	$245.91	7.737%	$264.9361	$264.94	$264.95	$264.90
Purchase #6	$63.67	6.231%	$67.6373	$67.64	$67.65	$67.60
Purchase #7	$238.82	11.873%	$267.1751	$267.18	$267.20	$267.20
7 purchase totals =	$1,140.25		$1,238.1248	$1,238.14	$1,238.15	$1,238.10