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	$235.38	12.795%	$265.4969	$265.50	$265.50	$265.50
Purchase #2	$33.69	9.231%	$36.7999	$36.80	$36.80	$36.80
Purchase #3	$9.30	8.745%	$10.1133	$10.11	$10.10	$10.10
Purchase #4	$206.52	7.322%	$221.6414	$221.64	$221.65	$221.60
Purchase #5	$75.34	4.422%	$78.6715	$78.67	$78.65	$78.70
Purchase #6	$140.96	9.874%	$154.8784	$154.88	$154.90	$154.90
Purchase #7	$79.74	12.601%	$89.788	$89.79	$89.80	$89.80
7 purchase totals =	$780.93		$857.3894	$857.39	$857.40	$857.40