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	$137.40	3.326%	$141.9699	$141.97	$141.95	$142.00
Purchase #2	$149.59	3.467%	$154.7763	$154.78	$154.80	$154.80
Purchase #3	$75.61	12.608%	$85.1429	$85.14	$85.15	$85.10
Purchase #4	$49.56	13.498%	$56.2496	$56.25	$56.25	$56.20
Purchase #5	$114.30	3.706%	$118.536	$118.54	$118.55	$118.50
Purchase #6	$88.76	7.476%	$95.3957	$95.40	$95.40	$95.40
Purchase #7	$171.56	6.154%	$182.1178	$182.12	$182.10	$182.10
7 purchase totals =	$786.78		$834.1882	$834.20	$834.20	$834.10