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	$55.79	12.382%	$62.6979	$62.70	$62.70	$62.70
Purchase #2	$149.46	12.562%	$168.2352	$168.24	$168.25	$168.20
Purchase #3	$189.64	3.776%	$196.8008	$196.80	$196.80	$196.80
Purchase #4	$30.30	10.195%	$33.3891	$33.39	$33.40	$33.40
Purchase #5	$40.79	10.843%	$45.2129	$45.21	$45.20	$45.20
Purchase #6	$202.57	6.753%	$216.2496	$216.25	$216.25	$216.20
Purchase #7	$196.47	8.842%	$213.8419	$213.84	$213.85	$213.80
7 purchase totals =	$865.02		$936.4274	$936.43	$936.45	$936.30