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	$97.32	8.214%	$105.3139	$105.31	$105.30	$105.30
Purchase #2	$47.57	11.467%	$53.0249	$53.02	$53.00	$53.00
Purchase #3	$83.51	6.765%	$89.1595	$89.16	$89.15	$89.20
Purchase #4	$245.47	11.334%	$273.2916	$273.29	$273.30	$273.30
Purchase #5	$212.25	10.653%	$234.861	$234.86	$234.85	$234.90
Purchase #6	$180.96	10.539%	$200.0314	$200.03	$200.05	$200.00
Purchase #7	$238.55	12.113%	$267.4456	$267.45	$267.45	$267.40
7 purchase totals =	$1,105.63		$1,223.1279	$1,223.12	$1,223.10	$1,223.10