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	$246.83	9.275%	$269.7235	$269.72	$269.70	$269.70
Purchase #2	$102.34	11.843%	$114.4601	$114.46	$114.45	$114.50
Purchase #3	$221.59	12.777%	$249.9026	$249.90	$249.90	$249.90
Purchase #4	$84.97	5.405%	$89.5626	$89.56	$89.55	$89.60
Purchase #5	$161.38	8.732%	$175.4717	$175.47	$175.45	$175.50
Purchase #6	$74.46	10.544%	$82.3111	$82.31	$82.30	$82.30
Purchase #7	$140.69	8.827%	$153.1087	$153.11	$153.10	$153.10
7 purchase totals =	$1,032.26		$1,134.5403	$1,134.53	$1,134.45	$1,134.60