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	$83.53	12.804%	$94.2252	$94.23	$94.25	$94.20
Purchase #2	$196.39	3.752%	$203.7586	$203.76	$203.75	$203.80
Purchase #3	$83.38	8.459%	$90.4331	$90.43	$90.45	$90.40
Purchase #4	$99.59	11.278%	$110.8218	$110.82	$110.80	$110.80
Purchase #5	$154.62	11.386%	$172.225	$172.23	$172.25	$172.20
Purchase #6	$139.74	13.434%	$158.5127	$158.51	$158.50	$158.50
Purchase #7	$77.40	13.554%	$87.8908	$87.89	$87.90	$87.90
7 purchase totals =	$834.65		$917.8672	$917.87	$917.90	$917.80