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	$25.67	12.614%	$28.908	$28.91	$28.90	$28.90
Purchase #2	$170.57	12.162%	$191.3147	$191.31	$191.30	$191.30
Purchase #3	$140.55	13.524%	$159.558	$159.56	$159.55	$159.60
Purchase #4	$186.73	12.229%	$209.5652	$209.57	$209.55	$209.60
Purchase #5	$157.85	4.465%	$164.898	$164.90	$164.90	$164.90
Purchase #6	$97.82	7.594%	$105.2485	$105.25	$105.25	$105.20
Purchase #7	$117.38	8.340%	$127.1695	$127.17	$127.15	$127.20
7 purchase totals =	$896.57		$986.6619	$986.67	$986.60	$986.70