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	$31.75	8.372%	$34.4081	$34.41	$34.40	$34.40
Purchase #2	$190.82	13.309%	$216.2162	$216.22	$216.20	$216.20
Purchase #3	$185.36	6.135%	$196.7318	$196.73	$196.75	$196.70
Purchase #4	$48.61	10.860%	$53.889	$53.89	$53.90	$53.90
Purchase #5	$49.31	13.141%	$55.7898	$55.79	$55.80	$55.80
Purchase #6	$5.29	3.631%	$5.4821	$5.48	$5.50	$5.50
Purchase #7	$136.70	10.584%	$151.1683	$151.17	$151.15	$151.20
7 purchase totals =	$647.84		$713.6853	$713.69	$713.70	$713.70