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	$35.88	9.600%	$39.3245	$39.32	$39.30	$39.30
Purchase #2	$144.43	10.234%	$159.211	$159.21	$159.20	$159.20
Purchase #3	$85.83	10.799%	$95.0988	$95.10	$95.10	$95.10
Purchase #4	$245.46	12.160%	$275.3079	$275.31	$275.30	$275.30
Purchase #5	$79.85	9.724%	$87.6146	$87.61	$87.60	$87.60
Purchase #6	$125.32	3.623%	$129.8603	$129.86	$129.85	$129.90
Purchase #7	$182.95	7.210%	$196.1407	$196.14	$196.15	$196.10
7 purchase totals =	$899.72		$982.5578	$982.55	$982.50	$982.50