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	$137.83	3.385%	$142.4955	$142.50	$142.50	$142.50
Purchase #2	$137.45	10.600%	$152.0197	$152.02	$152.00	$152.00
Purchase #3	$179.44	5.837%	$189.9139	$189.91	$189.90	$189.90
Purchase #4	$66.89	9.804%	$73.4479	$73.45	$73.45	$73.40
Purchase #5	$170.98	5.223%	$179.9103	$179.91	$179.90	$179.90
Purchase #6	$171.30	3.254%	$176.8741	$176.87	$176.85	$176.90
Purchase #7	$198.72	12.354%	$223.2699	$223.27	$223.25	$223.30
7 purchase totals =	$1,062.61		$1,137.9313	$1,137.93	$1,137.85	$1,137.90