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	$94.86	5.478%	$100.0564	$100.06	$100.05	$100.10
Purchase #2	$184.58	3.764%	$191.5276	$191.53	$191.55	$191.50
Purchase #3	$64.97	11.309%	$72.3175	$72.32	$72.30	$72.30
Purchase #4	$222.93	12.260%	$250.2612	$250.26	$250.25	$250.30
Purchase #5	$61.99	9.589%	$67.9342	$67.93	$67.95	$67.90
Purchase #6	$216.35	9.326%	$236.5268	$236.53	$236.55	$236.50
Purchase #7	$217.80	4.336%	$227.2438	$227.24	$227.25	$227.20
7 purchase totals =	$1,063.48		$1,145.8675	$1,145.87	$1,145.90	$1,145.80