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	$120.74	8.783%	$131.3446	$131.34	$131.35	$131.30
Purchase #2	$126.91	3.347%	$131.1577	$131.16	$131.15	$131.20
Purchase #3	$36.59	13.740%	$41.6175	$41.62	$41.60	$41.60
Purchase #4	$99.34	3.492%	$102.809	$102.81	$102.80	$102.80
Purchase #5	$222.79	6.809%	$237.9598	$237.96	$237.95	$238.00
Purchase #6	$124.41	11.405%	$138.599	$138.60	$138.60	$138.60
Purchase #7	$43.85	11.503%	$48.8941	$48.89	$48.90	$48.90
7 purchase totals =	$774.63		$832.3817	$832.38	$832.35	$832.40