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	$86.93	13.348%	$98.5334	$98.53	$98.55	$98.50
Purchase #2	$105.52	10.500%	$116.5996	$116.60	$116.60	$116.60
Purchase #3	$36.49	6.598%	$38.8976	$38.90	$38.90	$38.90
Purchase #4	$100.60	11.731%	$112.4014	$112.40	$112.40	$112.40
Purchase #5	$188.47	3.419%	$194.9138	$194.91	$194.90	$194.90
Purchase #6	$37.46	6.107%	$39.7477	$39.75	$39.75	$39.70
Purchase #7	$67.69	7.353%	$72.6672	$72.67	$72.65	$72.70
7 purchase totals =	$623.16		$673.7607	$673.76	$673.75	$673.70