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	$35.76	5.112%	$37.5881	$37.59	$37.60	$37.60
Purchase #2	$232.33	11.433%	$258.8923	$258.89	$258.90	$258.90
Purchase #3	$123.97	6.310%	$131.7925	$131.79	$131.80	$131.80
Purchase #4	$71.42	10.629%	$79.0112	$79.01	$79.00	$79.00
Purchase #5	$62.82	9.258%	$68.6359	$68.64	$68.65	$68.60
Purchase #6	$68.46	9.867%	$75.2149	$75.21	$75.20	$75.20
Purchase #7	$184.81	6.560%	$196.9335	$196.93	$196.95	$196.90
7 purchase totals =	$779.57		$848.0684	$848.06	$848.10	$848.00