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	$75.37	6.606%	$80.3489	$80.35	$80.35	$80.30
Purchase #2	$219.71	9.401%	$240.3649	$240.36	$240.35	$240.40
Purchase #3	$210.63	6.199%	$223.687	$223.69	$223.70	$223.70
Purchase #4	$132.72	7.831%	$143.1133	$143.11	$143.10	$143.10
Purchase #5	$72.28	6.243%	$76.7924	$76.79	$76.80	$76.80
Purchase #6	$50.74	6.204%	$53.8879	$53.89	$53.90	$53.90
Purchase #7	$39.42	6.833%	$42.1136	$42.11	$42.10	$42.10
7 purchase totals =	$800.87		$860.3080	$860.30	$860.30	$860.30