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	$234.31	5.604%	$247.4407	$247.44	$247.45	$247.40
Purchase #2	$89.61	11.393%	$99.8193	$99.82	$99.80	$99.80
Purchase #3	$172.82	10.522%	$191.0041	$191.00	$191.00	$191.00
Purchase #4	$152.82	7.862%	$164.8347	$164.83	$164.85	$164.80
Purchase #5	$168.85	8.168%	$182.6417	$182.64	$182.65	$182.60
Purchase #6	$75.36	10.275%	$83.1032	$83.10	$83.10	$83.10
Purchase #7	$213.88	7.457%	$229.829	$229.83	$229.85	$229.80
7 purchase totals =	$1,107.65		$1,198.6727	$1,198.66	$1,198.70	$1,198.50