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	$66.69	9.302%	$72.8935	$72.89	$72.90	$72.90
Purchase #2	$141.34	12.536%	$159.0584	$159.06	$159.05	$159.10
Purchase #3	$106.88	3.300%	$110.407	$110.41	$110.40	$110.40
Purchase #4	$84.74	13.863%	$96.4875	$96.49	$96.50	$96.50
Purchase #5	$38.71	11.428%	$43.1338	$43.13	$43.15	$43.10
Purchase #6	$153.95	4.161%	$160.3559	$160.36	$160.35	$160.40
Purchase #7	$76.64	12.385%	$86.1319	$86.13	$86.15	$86.10
7 purchase totals =	$668.95		$728.4680	$728.47	$728.50	$728.50