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	$88.79	11.577%	$99.0692	$99.07	$99.05	$99.10
Purchase #2	$224.35	6.190%	$238.2373	$238.24	$238.25	$238.20
Purchase #3	$90.50	7.393%	$97.1907	$97.19	$97.20	$97.20
Purchase #4	$157.31	3.222%	$162.3785	$162.38	$162.40	$162.40
Purchase #5	$61.71	9.352%	$67.4811	$67.48	$67.50	$67.50
Purchase #6	$215.27	7.683%	$231.8092	$231.81	$231.80	$231.80
Purchase #7	$134.75	4.470%	$140.7733	$140.77	$140.75	$140.80
7 purchase totals =	$972.68		$1,036.9393	$1,036.94	$1,036.95	$1,037.00