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	$100.87	9.386%	$110.3377	$110.34	$110.35	$110.30
Purchase #2	$78.33	10.364%	$86.4481	$86.45	$86.45	$86.40
Purchase #3	$73.39	4.868%	$76.9626	$76.96	$76.95	$77.00
Purchase #4	$33.36	13.855%	$37.982	$37.98	$38.00	$38.00
Purchase #5	$83.90	12.662%	$94.5234	$94.52	$94.50	$94.50
Purchase #6	$45.27	13.190%	$51.2411	$51.24	$51.25	$51.20
Purchase #7	$49.31	7.186%	$52.8534	$52.85	$52.85	$52.90
7 purchase totals =	$464.43		$510.3483	$510.34	$510.35	$510.30