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	$7.43	6.571%	$7.9182	$7.92	$7.90	$7.90
Purchase #2	$113.75	12.351%	$127.7993	$127.80	$127.80	$127.80
Purchase #3	$67.73	4.631%	$70.8666	$70.87	$70.85	$70.90
Purchase #4	$81.55	4.648%	$85.3404	$85.34	$85.35	$85.30
Purchase #5	$65.67	10.143%	$72.3309	$72.33	$72.35	$72.30
Purchase #6	$250.41	9.403%	$273.9561	$273.96	$273.95	$274.00
Purchase #7	$166.29	11.611%	$185.5979	$185.60	$185.60	$185.60
7 purchase totals =	$752.83		$823.8094	$823.82	$823.80	$823.80