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	$91.25	12.599%	$102.7466	$102.75	$102.75	$102.70
Purchase #2	$32.76	3.138%	$33.788	$33.79	$33.80	$33.80
Purchase #3	$36.46	12.283%	$40.9384	$40.94	$40.95	$40.90
Purchase #4	$191.50	5.676%	$202.3695	$202.37	$202.35	$202.40
Purchase #5	$139.27	4.377%	$145.3658	$145.37	$145.35	$145.40
Purchase #6	$38.73	9.253%	$42.3137	$42.31	$42.30	$42.30
Purchase #7	$130.33	11.225%	$144.9595	$144.96	$144.95	$145.00
7 purchase totals =	$660.30		$712.4815	$712.49	$712.45	$712.50