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	$101.34	9.739%	$111.2095	$111.21	$111.20	$111.20
Purchase #2	$31.62	11.829%	$35.3603	$35.36	$35.35	$35.40
Purchase #3	$136.26	8.312%	$147.5859	$147.59	$147.60	$147.60
Purchase #4	$225.72	7.708%	$243.1185	$243.12	$243.10	$243.10
Purchase #5	$80.61	10.373%	$88.9717	$88.97	$88.95	$89.00
Purchase #6	$86.47	4.404%	$90.2781	$90.28	$90.30	$90.30
Purchase #7	$209.89	10.326%	$231.5632	$231.56	$231.55	$231.60
7 purchase totals =	$871.91		$948.0872	$948.09	$948.05	$948.20