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	$27.60	9.240%	$30.1502	$30.15	$30.15	$30.20
Purchase #2	$160.54	12.217%	$180.1532	$180.15	$180.15	$180.20
Purchase #3	$164.74	12.498%	$185.3292	$185.33	$185.35	$185.30
Purchase #4	$28.60	8.438%	$31.0133	$31.01	$31.00	$31.00
Purchase #5	$175.46	12.202%	$196.8696	$196.87	$196.85	$196.90
Purchase #6	$199.28	12.112%	$223.4168	$223.42	$223.40	$223.40
Purchase #7	$187.33	6.402%	$199.3229	$199.32	$199.30	$199.30
7 purchase totals =	$943.55		$1,046.2552	$1,046.25	$1,046.20	$1,046.30