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	$107.27	12.433%	$120.6069	$120.61	$120.60	$120.60
Purchase #2	$40.96	3.372%	$42.3412	$42.34	$42.35	$42.30
Purchase #3	$180.45	11.242%	$200.7362	$200.74	$200.75	$200.70
Purchase #4	$250.31	12.135%	$280.6851	$280.69	$280.70	$280.70
Purchase #5	$182.71	10.506%	$201.9055	$201.91	$201.90	$201.90
Purchase #6	$49.29	7.601%	$53.0365	$53.04	$53.05	$53.00
Purchase #7	$106.62	10.674%	$118.0006	$118.00	$118.00	$118.00
7 purchase totals =	$917.61		$1,017.3120	$1,017.33	$1,017.35	$1,017.20