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	$45.80	3.794%	$47.5377	$47.54	$47.55	$47.50
Purchase #2	$213.72	4.503%	$223.3438	$223.34	$223.35	$223.30
Purchase #3	$247.34	13.543%	$280.8373	$280.84	$280.85	$280.80
Purchase #4	$135.56	8.527%	$147.1192	$147.12	$147.10	$147.10
Purchase #5	$146.61	3.112%	$151.1725	$151.17	$151.15	$151.20
Purchase #6	$218.62	12.236%	$245.3703	$245.37	$245.35	$245.40
Purchase #7	$147.42	11.475%	$164.3364	$164.34	$164.35	$164.30
7 purchase totals =	$1,155.07		$1,259.7172	$1,259.72	$1,259.70	$1,259.60