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	$44.96	11.275%	$50.0292	$50.03	$50.05	$50.00
Purchase #2	$130.31	8.118%	$140.8886	$140.89	$140.90	$140.90
Purchase #3	$200.63	7.385%	$215.4465	$215.45	$215.45	$215.40
Purchase #4	$94.82	10.230%	$104.5201	$104.52	$104.50	$104.50
Purchase #5	$169.99	12.866%	$191.8609	$191.86	$191.85	$191.90
Purchase #6	$96.71	13.234%	$109.5086	$109.51	$109.50	$109.50
Purchase #7	$210.87	7.364%	$226.3985	$226.40	$226.40	$226.40
7 purchase totals =	$948.29		$1,038.6524	$1,038.66	$1,038.65	$1,038.60