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	$77.94	3.324%	$80.5307	$80.53	$80.55	$80.50
Purchase #2	$243.61	12.339%	$273.669	$273.67	$273.65	$273.70
Purchase #3	$7.72	10.277%	$8.5134	$8.51	$8.50	$8.50
Purchase #4	$232.53	5.594%	$245.5377	$245.54	$245.55	$245.50
Purchase #5	$172.56	11.165%	$191.8263	$191.83	$191.85	$191.80
Purchase #6	$54.89	7.635%	$59.0809	$59.08	$59.10	$59.10
Purchase #7	$102.80	9.152%	$112.2083	$112.21	$112.20	$112.20
7 purchase totals =	$892.05		$971.3663	$971.37	$971.40	$971.30