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	$167.55	7.464%	$180.0559	$180.06	$180.05	$180.10
Purchase #2	$25.39	11.772%	$28.3789	$28.38	$28.40	$28.40
Purchase #3	$248.45	6.631%	$264.9247	$264.92	$264.90	$264.90
Purchase #4	$166.71	11.114%	$185.2381	$185.24	$185.25	$185.20
Purchase #5	$249.85	12.272%	$280.5116	$280.51	$280.50	$280.50
Purchase #6	$98.26	3.235%	$101.4387	$101.44	$101.45	$101.40
Purchase #7	$106.34	6.417%	$113.1638	$113.16	$113.15	$113.20
7 purchase totals =	$1,062.55		$1,153.7117	$1,153.71	$1,153.70	$1,153.70