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	$71.30	3.678%	$73.9224	$73.92	$73.90	$73.90
Purchase #2	$39.83	11.610%	$44.4543	$44.45	$44.45	$44.50
Purchase #3	$85.66	12.735%	$96.5688	$96.57	$96.55	$96.60
Purchase #4	$134.42	3.455%	$139.0642	$139.06	$139.05	$139.10
Purchase #5	$35.94	4.473%	$37.5476	$37.55	$37.55	$37.50
Purchase #6	$13.71	8.334%	$14.8526	$14.85	$14.85	$14.90
Purchase #7	$84.33	11.669%	$94.1705	$94.17	$94.15	$94.20
7 purchase totals =	$465.19		$500.5804	$500.57	$500.50	$500.70