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	$75.82	11.569%	$84.5916	$84.59	$84.60	$84.60
Purchase #2	$174.56	4.534%	$182.4746	$182.47	$182.45	$182.50
Purchase #3	$212.66	10.598%	$235.1977	$235.20	$235.20	$235.20
Purchase #4	$195.63	13.779%	$222.5859	$222.59	$222.60	$222.60
Purchase #5	$40.44	5.104%	$42.5041	$42.50	$42.50	$42.50
Purchase #6	$90.94	5.815%	$96.2282	$96.23	$96.25	$96.20
Purchase #7	$170.30	9.492%	$186.4649	$186.46	$186.45	$186.50
7 purchase totals =	$960.35		$1,050.0470	$1,050.04	$1,050.05	$1,050.10