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	$30.71	3.209%	$31.6955	$31.70	$31.70	$31.70
Purchase #2	$154.40	8.197%	$167.0562	$167.06	$167.05	$167.10
Purchase #3	$173.48	12.347%	$194.8996	$194.90	$194.90	$194.90
Purchase #4	$52.82	12.407%	$59.3734	$59.37	$59.35	$59.40
Purchase #5	$67.89	9.250%	$74.1698	$74.17	$74.15	$74.20
Purchase #6	$47.62	5.678%	$50.3239	$50.32	$50.30	$50.30
Purchase #7	$235.80	3.223%	$243.3998	$243.40	$243.40	$243.40
7 purchase totals =	$762.72		$820.9182	$820.92	$820.85	$821.00