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	$232.41	9.180%	$253.7452	$253.75	$253.75	$253.70
Purchase #2	$78.59	4.607%	$82.2106	$82.21	$82.20	$82.20
Purchase #3	$42.31	8.349%	$45.8425	$45.84	$45.85	$45.80
Purchase #4	$173.55	4.205%	$180.8478	$180.85	$180.85	$180.80
Purchase #5	$127.27	9.362%	$139.185	$139.19	$139.20	$139.20
Purchase #6	$123.56	11.481%	$137.7459	$137.75	$137.75	$137.70
Purchase #7	$79.69	6.677%	$85.0109	$85.01	$85.00	$85.00
7 purchase totals =	$857.38		$924.5879	$924.60	$924.60	$924.40