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	$137.51	6.537%	$146.499	$146.50	$146.50	$146.50
Purchase #2	$82.88	10.787%	$91.8203	$91.82	$91.80	$91.80
Purchase #3	$30.46	7.818%	$32.8414	$32.84	$32.85	$32.80
Purchase #4	$59.75	7.708%	$64.3555	$64.36	$64.35	$64.40
Purchase #5	$119.45	3.111%	$123.1661	$123.17	$123.15	$123.20
Purchase #6	$181.94	12.275%	$204.2731	$204.27	$204.25	$204.30
Purchase #7	$187.77	12.659%	$211.5398	$211.54	$211.55	$211.50
7 purchase totals =	$799.76		$874.4952	$874.50	$874.45	$874.50