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	$66.46	4.137%	$69.2095	$69.21	$69.20	$69.20
Purchase #2	$94.66	12.212%	$106.2199	$106.22	$106.20	$106.20
Purchase #3	$160.59	6.819%	$171.5406	$171.54	$171.55	$171.50
Purchase #4	$67.91	6.485%	$72.314	$72.31	$72.30	$72.30
Purchase #5	$20.63	3.409%	$21.3333	$21.33	$21.35	$21.30
Purchase #6	$233.69	6.368%	$248.5714	$248.57	$248.55	$248.60
Purchase #7	$81.50	9.715%	$89.4177	$89.42	$89.40	$89.40
7 purchase totals =	$725.44		$778.6064	$778.60	$778.55	$778.50