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	$132.90	5.273%	$139.9078	$139.91	$139.90	$139.90
Purchase #2	$112.62	10.254%	$124.1681	$124.17	$124.15	$124.20
Purchase #3	$109.71	5.589%	$115.8417	$115.84	$115.85	$115.80
Purchase #4	$56.95	3.799%	$59.1135	$59.11	$59.10	$59.10
Purchase #5	$141.80	10.770%	$157.0719	$157.07	$157.05	$157.10
Purchase #6	$98.72	13.678%	$112.2229	$112.22	$112.20	$112.20
Purchase #7	$30.64	9.751%	$33.6277	$33.63	$33.65	$33.60
7 purchase totals =	$683.34		$741.9536	$741.95	$741.90	$741.90