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	$135.34	6.679%	$144.3794	$144.38	$144.40	$144.40
Purchase #2	$61.30	10.804%	$67.9229	$67.92	$67.90	$67.90
Purchase #3	$54.48	3.751%	$56.5235	$56.52	$56.50	$56.50
Purchase #4	$153.45	3.312%	$158.5323	$158.53	$158.55	$158.50
Purchase #5	$187.43	7.226%	$200.9737	$200.97	$200.95	$201.00
Purchase #6	$68.33	5.320%	$71.9652	$71.97	$71.95	$72.00
Purchase #7	$77.37	7.432%	$83.1201	$83.12	$83.10	$83.10
7 purchase totals =	$737.70		$783.4171	$783.41	$783.35	$783.40