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	$68.36	13.418%	$77.5325	$77.53	$77.55	$77.50
Purchase #2	$27.96	13.125%	$31.6298	$31.63	$31.65	$31.60
Purchase #3	$141.91	7.381%	$152.3844	$152.38	$152.40	$152.40
Purchase #4	$78.45	13.425%	$88.9819	$88.98	$89.00	$89.00
Purchase #5	$219.28	9.428%	$239.9537	$239.95	$239.95	$240.00
Purchase #6	$54.41	6.387%	$57.8852	$57.89	$57.90	$57.90
Purchase #7	$19.93	12.756%	$22.4723	$22.47	$22.45	$22.50
7 purchase totals =	$610.30		$670.8398	$670.83	$670.90	$670.90