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	$209.42	8.560%	$227.3464	$227.35	$227.35	$227.30
Purchase #2	$180.86	10.320%	$199.5248	$199.52	$199.50	$199.50
Purchase #3	$150.92	12.865%	$170.3359	$170.34	$170.35	$170.30
Purchase #4	$145.47	3.740%	$150.9106	$150.91	$150.90	$150.90
Purchase #5	$173.38	5.447%	$182.824	$182.82	$182.80	$182.80
Purchase #6	$55.71	8.261%	$60.3122	$60.31	$60.30	$60.30
Purchase #7	$92.81	7.703%	$99.9592	$99.96	$99.95	$100.00
7 purchase totals =	$1,008.57		$1,091.2131	$1,091.21	$1,091.15	$1,091.10