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	$120.85	6.424%	$128.6134	$128.61	$128.60	$128.60
Purchase #2	$247.94	6.791%	$264.7776	$264.78	$264.80	$264.80
Purchase #3	$166.82	13.518%	$189.3707	$189.37	$189.35	$189.40
Purchase #4	$7.33	4.655%	$7.6712	$7.67	$7.65	$7.70
Purchase #5	$162.99	3.371%	$168.4844	$168.48	$168.50	$168.50
Purchase #6	$245.73	11.734%	$274.564	$274.56	$274.55	$274.60
Purchase #7	$5.35	10.248%	$5.8983	$5.90	$5.90	$5.90
7 purchase totals =	$957.01		$1,039.3796	$1,039.37	$1,039.35	$1,039.50