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	$37.81	5.213%	$39.781	$39.78	$39.80	$39.80
Purchase #2	$129.56	13.804%	$147.4445	$147.44	$147.45	$147.40
Purchase #3	$226.89	3.345%	$234.4795	$234.48	$234.50	$234.50
Purchase #4	$109.27	8.212%	$118.2433	$118.24	$118.25	$118.20
Purchase #5	$176.38	6.761%	$188.3051	$188.31	$188.30	$188.30
Purchase #6	$202.34	9.115%	$220.7833	$220.78	$220.80	$220.80
Purchase #7	$216.34	7.173%	$231.8581	$231.86	$231.85	$231.90
7 purchase totals =	$1,098.59		$1,180.8948	$1,180.89	$1,180.95	$1,180.90