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	$134.87	9.301%	$147.4143	$147.41	$147.40	$147.40
Purchase #2	$110.78	12.216%	$124.3129	$124.31	$124.30	$124.30
Purchase #3	$134.72	3.472%	$139.3975	$139.40	$139.40	$139.40
Purchase #4	$192.95	12.194%	$216.4783	$216.48	$216.50	$216.50
Purchase #5	$78.43	8.534%	$85.1232	$85.12	$85.10	$85.10
Purchase #6	$177.75	12.114%	$199.2826	$199.28	$199.30	$199.30
Purchase #7	$65.91	9.457%	$72.1431	$72.14	$72.15	$72.10
7 purchase totals =	$895.41		$984.1519	$984.14	$984.15	$984.10