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	$147.60	12.827%	$166.5327	$166.53	$166.55	$166.50
Purchase #2	$79.78	7.214%	$85.5353	$85.54	$85.55	$85.50
Purchase #3	$9.33	12.383%	$10.4853	$10.49	$10.50	$10.50
Purchase #4	$200.29	11.339%	$223.0009	$223.00	$223.00	$223.00
Purchase #5	$245.69	11.738%	$274.5291	$274.53	$274.55	$274.50
Purchase #6	$149.95	3.193%	$154.7379	$154.74	$154.75	$154.70
Purchase #7	$72.67	13.511%	$82.4884	$82.49	$82.50	$82.50
7 purchase totals =	$905.31		$997.3096	$997.32	$997.40	$997.20