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	$107.89	12.441%	$121.3126	$121.31	$121.30	$121.30
Purchase #2	$84.78	7.174%	$90.8621	$90.86	$90.85	$90.90
Purchase #3	$144.60	4.833%	$151.5885	$151.59	$151.60	$151.60
Purchase #4	$227.80	11.525%	$254.054	$254.05	$254.05	$254.10
Purchase #5	$73.38	12.524%	$82.5701	$82.57	$82.55	$82.60
Purchase #6	$181.54	5.479%	$191.4866	$191.49	$191.50	$191.50
Purchase #7	$203.49	8.391%	$220.5648	$220.56	$220.55	$220.60
7 purchase totals =	$1,023.48		$1,112.4387	$1,112.43	$1,112.40	$1,112.60