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	$215.46	3.595%	$223.2058	$223.21	$223.20	$223.20
Purchase #2	$71.44	12.293%	$80.2221	$80.22	$80.20	$80.20
Purchase #3	$68.66	7.207%	$73.6083	$73.61	$73.60	$73.60
Purchase #4	$174.29	4.710%	$182.4991	$182.50	$182.50	$182.50
Purchase #5	$18.88	11.534%	$21.0576	$21.06	$21.05	$21.10
Purchase #6	$82.45	4.661%	$86.293	$86.29	$86.30	$86.30
Purchase #7	$99.71	9.624%	$109.3061	$109.31	$109.30	$109.30
7 purchase totals =	$730.89		$776.1920	$776.20	$776.15	$776.20