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	$80.27	12.478%	$90.2861	$90.29	$90.30	$90.30
Purchase #2	$143.75	11.511%	$160.2971	$160.30	$160.30	$160.30
Purchase #3	$27.85	11.247%	$30.9823	$30.98	$31.00	$31.00
Purchase #4	$246.45	8.386%	$267.1173	$267.12	$267.10	$267.10
Purchase #5	$147.89	12.111%	$165.801	$165.80	$165.80	$165.80
Purchase #6	$96.87	8.570%	$105.1718	$105.17	$105.15	$105.20
Purchase #7	$171.89	7.150%	$184.1801	$184.18	$184.20	$184.20
7 purchase totals =	$914.97		$1,003.8357	$1,003.84	$1,003.85	$1,003.90