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	$169.47	11.593%	$189.1167	$189.12	$189.10	$189.10
Purchase #2	$50.54	13.534%	$57.3801	$57.38	$57.40	$57.40
Purchase #3	$37.69	11.711%	$42.1039	$42.10	$42.10	$42.10
Purchase #4	$119.67	9.797%	$131.3941	$131.39	$131.40	$131.40
Purchase #5	$47.27	8.187%	$51.14	$51.14	$51.15	$51.10
Purchase #6	$221.55	8.697%	$240.8182	$240.82	$240.80	$240.80
Purchase #7	$126.86	7.361%	$136.1982	$136.20	$136.20	$136.20
7 purchase totals =	$773.05		$848.1512	$848.15	$848.15	$848.10