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	$51.75	11.807%	$57.8601	$57.86	$57.85	$57.90
Purchase #2	$175.92	3.820%	$182.6401	$182.64	$182.65	$182.60
Purchase #3	$221.34	12.431%	$248.8548	$248.85	$248.85	$248.90
Purchase #4	$226.84	4.503%	$237.0546	$237.05	$237.05	$237.10
Purchase #5	$72.27	8.567%	$78.4614	$78.46	$78.45	$78.50
Purchase #6	$205.85	4.401%	$214.9095	$214.91	$214.90	$214.90
Purchase #7	$162.33	4.615%	$169.8215	$169.82	$169.80	$169.80
7 purchase totals =	$1,116.30		$1,189.6020	$1,189.59	$1,189.55	$1,189.70