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	$53.68	13.386%	$60.8656	$60.87	$60.85	$60.90
Purchase #2	$246.69	7.369%	$264.8686	$264.87	$264.85	$264.90
Purchase #3	$169.88	11.774%	$189.8817	$189.88	$189.90	$189.90
Purchase #4	$62.55	6.620%	$66.6908	$66.69	$66.70	$66.70
Purchase #5	$6.65	12.761%	$7.4986	$7.50	$7.50	$7.50
Purchase #6	$219.71	7.215%	$235.5621	$235.56	$235.55	$235.60
Purchase #7	$161.60	4.336%	$168.607	$168.61	$168.60	$168.60
7 purchase totals =	$920.76		$993.9744	$993.98	$993.95	$994.10