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	$51.42	9.637%	$56.3753	$56.38	$56.40	$56.40
Purchase #2	$156.61	3.442%	$162.0005	$162.00	$162.00	$162.00
Purchase #3	$160.46	6.348%	$170.646	$170.65	$170.65	$170.60
Purchase #4	$67.32	4.439%	$70.3083	$70.31	$70.30	$70.30
Purchase #5	$205.35	6.331%	$218.3507	$218.35	$218.35	$218.40
Purchase #6	$160.33	11.213%	$178.3078	$178.31	$178.30	$178.30
Purchase #7	$130.85	4.616%	$136.89	$136.89	$136.90	$136.90
7 purchase totals =	$932.34		$992.8786	$992.89	$992.90	$992.90