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	$199.57	9.441%	$218.4114	$218.41	$218.40	$218.40
Purchase #2	$146.44	10.777%	$162.2218	$162.22	$162.20	$162.20
Purchase #3	$77.26	10.782%	$85.5902	$85.59	$85.60	$85.60
Purchase #4	$192.92	11.680%	$215.4531	$215.45	$215.45	$215.50
Purchase #5	$30.36	7.200%	$32.5459	$32.55	$32.55	$32.50
Purchase #6	$138.82	6.288%	$147.549	$147.55	$147.55	$147.50
Purchase #7	$38.55	11.711%	$43.0646	$43.06	$43.05	$43.10
7 purchase totals =	$823.92		$904.8360	$904.83	$904.80	$904.80