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	$81.69	9.367%	$89.3419	$89.34	$89.35	$89.30
Purchase #2	$176.54	12.774%	$199.0912	$199.09	$199.10	$199.10
Purchase #3	$67.57	13.786%	$76.8852	$76.89	$76.90	$76.90
Purchase #4	$77.26	6.173%	$82.0293	$82.03	$82.05	$82.00
Purchase #5	$250.92	5.678%	$265.1672	$265.17	$265.15	$265.20
Purchase #6	$201.43	6.120%	$213.7575	$213.76	$213.75	$213.80
Purchase #7	$168.42	13.763%	$191.5996	$191.60	$191.60	$191.60
7 purchase totals =	$1,023.83		$1,117.8719	$1,117.88	$1,117.90	$1,117.90