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	$104.73	7.392%	$112.4716	$112.47	$112.45	$112.50
Purchase #2	$91.90	8.681%	$99.8778	$99.88	$99.90	$99.90
Purchase #3	$115.56	8.438%	$125.311	$125.31	$125.30	$125.30
Purchase #4	$66.90	4.215%	$69.7198	$69.72	$69.70	$69.70
Purchase #5	$137.27	12.203%	$154.0211	$154.02	$154.00	$154.00
Purchase #6	$53.79	12.419%	$60.4702	$60.47	$60.45	$60.50
Purchase #7	$72.35	8.241%	$78.3124	$78.31	$78.30	$78.30
7 purchase totals =	$642.50		$700.1839	$700.18	$700.10	$700.20