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	$27.32	6.116%	$28.9909	$28.99	$29.00	$29.00
Purchase #2	$39.99	8.810%	$43.5131	$43.51	$43.50	$43.50
Purchase #3	$59.45	3.528%	$61.5474	$61.55	$61.55	$61.50
Purchase #4	$221.48	12.837%	$249.9114	$249.91	$249.90	$249.90
Purchase #5	$162.66	12.417%	$182.8575	$182.86	$182.85	$182.90
Purchase #6	$178.67	7.732%	$192.4848	$192.48	$192.50	$192.50
Purchase #7	$88.76	8.740%	$96.5176	$96.52	$96.50	$96.50
7 purchase totals =	$778.33		$855.8227	$855.82	$855.80	$855.80