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	$28.27	10.263%	$31.1714	$31.17	$31.15	$31.20
Purchase #2	$33.54	10.558%	$37.0812	$37.08	$37.10	$37.10
Purchase #3	$166.96	10.319%	$184.1886	$184.19	$184.20	$184.20
Purchase #4	$164.51	4.486%	$171.8899	$171.89	$171.90	$171.90
Purchase #5	$124.69	12.670%	$140.4882	$140.49	$140.50	$140.50
Purchase #6	$66.40	8.848%	$72.2751	$72.28	$72.30	$72.30
Purchase #7	$5.91	11.737%	$6.6037	$6.60	$6.60	$6.60
7 purchase totals =	$590.28		$643.6981	$643.70	$643.75	$643.80