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	$18.43	11.111%	$20.4778	$20.48	$20.50	$20.50
Purchase #2	$218.37	12.854%	$246.4393	$246.44	$246.45	$246.40
Purchase #3	$244.45	7.815%	$263.5538	$263.55	$263.55	$263.60
Purchase #4	$223.39	7.651%	$240.4816	$240.48	$240.50	$240.50
Purchase #5	$156.38	3.606%	$162.0191	$162.02	$162.00	$162.00
Purchase #6	$230.72	6.465%	$245.636	$245.64	$245.65	$245.60
Purchase #7	$141.51	12.122%	$158.6638	$158.66	$158.65	$158.70
7 purchase totals =	$1,233.25		$1,337.2714	$1,337.27	$1,337.30	$1,337.30