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	$82.61	8.651%	$89.7566	$89.76	$89.75	$89.80
Purchase #2	$65.87	4.809%	$69.0377	$69.04	$69.05	$69.00
Purchase #3	$83.37	8.346%	$90.3281	$90.33	$90.35	$90.30
Purchase #4	$47.94	12.737%	$54.0461	$54.05	$54.05	$54.00
Purchase #5	$45.77	12.193%	$51.3507	$51.35	$51.35	$51.40
Purchase #6	$48.30	6.375%	$51.3791	$51.38	$51.40	$51.40
Purchase #7	$112.99	5.506%	$119.2112	$119.21	$119.20	$119.20
7 purchase totals =	$486.85		$525.1095	$525.12	$525.15	$525.10