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	$150.51	6.452%	$160.2209	$160.22	$160.20	$160.20
Purchase #2	$245.79	7.725%	$264.7773	$264.78	$264.80	$264.80
Purchase #3	$147.33	12.510%	$165.761	$165.76	$165.75	$165.80
Purchase #4	$93.58	8.854%	$101.8656	$101.87	$101.85	$101.90
Purchase #5	$38.25	10.790%	$42.3772	$42.38	$42.40	$42.40
Purchase #6	$82.32	4.459%	$85.9906	$85.99	$86.00	$86.00
Purchase #7	$25.98	4.565%	$27.166	$27.17	$27.15	$27.20
7 purchase totals =	$783.76		$848.1586	$848.17	$848.15	$848.30