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	$213.30	7.160%	$228.5723	$228.57	$228.55	$228.60
Purchase #2	$149.54	13.662%	$169.9702	$169.97	$169.95	$170.00
Purchase #3	$223.83	9.870%	$245.922	$245.92	$245.90	$245.90
Purchase #4	$83.45	6.718%	$89.0562	$89.06	$89.05	$89.10
Purchase #5	$192.59	8.661%	$209.2702	$209.27	$209.25	$209.30
Purchase #6	$55.39	12.334%	$62.2218	$62.22	$62.20	$62.20
Purchase #7	$96.86	13.710%	$110.1395	$110.14	$110.15	$110.10
7 purchase totals =	$1,014.96		$1,115.1522	$1,115.15	$1,115.05	$1,115.20