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	$170.87	6.439%	$181.8723	$181.87	$181.85	$181.90
Purchase #2	$41.86	12.840%	$47.2348	$47.23	$47.25	$47.20
Purchase #3	$162.91	4.283%	$169.8874	$169.89	$169.90	$169.90
Purchase #4	$248.78	10.595%	$275.1382	$275.14	$275.15	$275.10
Purchase #5	$167.96	7.693%	$180.8812	$180.88	$180.90	$180.90
Purchase #6	$37.75	10.530%	$41.7251	$41.73	$41.75	$41.70
Purchase #7	$77.89	11.615%	$86.9369	$86.94	$86.95	$86.90
7 purchase totals =	$908.02		$983.6759	$983.68	$983.75	$983.60