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	$125.57	4.773%	$131.5635	$131.56	$131.55	$131.60
Purchase #2	$53.96	6.154%	$57.2807	$57.28	$57.30	$57.30
Purchase #3	$231.67	6.342%	$246.3625	$246.36	$246.35	$246.40
Purchase #4	$44.29	8.839%	$48.2048	$48.20	$48.20	$48.20
Purchase #5	$112.57	9.538%	$123.3069	$123.31	$123.30	$123.30
Purchase #6	$104.89	4.115%	$109.2062	$109.21	$109.20	$109.20
Purchase #7	$141.64	4.233%	$147.6356	$147.64	$147.65	$147.60
7 purchase totals =	$814.59		$863.5602	$863.56	$863.55	$863.60