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	$124.72	9.532%	$136.6083	$136.61	$136.60	$136.60
Purchase #2	$80.32	11.434%	$89.5038	$89.50	$89.50	$89.50
Purchase #3	$40.89	10.670%	$45.253	$45.25	$45.25	$45.30
Purchase #4	$45.77	6.515%	$48.7519	$48.75	$48.75	$48.80
Purchase #5	$28.38	6.102%	$30.1117	$30.11	$30.10	$30.10
Purchase #6	$135.78	12.311%	$152.4959	$152.50	$152.50	$152.50
Purchase #7	$88.90	5.568%	$93.85	$93.85	$93.85	$93.90
7 purchase totals =	$544.76		$596.5746	$596.57	$596.55	$596.70