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	$84.33	6.478%	$89.7929	$89.79	$89.80	$89.80
Purchase #2	$39.94	6.739%	$42.6316	$42.63	$42.65	$42.60
Purchase #3	$164.41	13.109%	$185.9625	$185.96	$185.95	$186.00
Purchase #4	$46.50	11.436%	$51.8177	$51.82	$51.80	$51.80
Purchase #5	$250.57	5.607%	$264.6195	$264.62	$264.60	$264.60
Purchase #6	$248.73	11.471%	$277.2618	$277.26	$277.25	$277.30
Purchase #7	$174.87	7.688%	$188.314	$188.31	$188.30	$188.30
7 purchase totals =	$1,009.35		$1,100.4000	$1,100.39	$1,100.35	$1,100.40