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	$168.35	8.649%	$182.9106	$182.91	$182.90	$182.90
Purchase #2	$41.98	6.628%	$44.7624	$44.76	$44.75	$44.80
Purchase #3	$196.87	9.405%	$215.3856	$215.39	$215.40	$215.40
Purchase #4	$33.32	12.277%	$37.4107	$37.41	$37.40	$37.40
Purchase #5	$220.46	13.562%	$250.3588	$250.36	$250.35	$250.40
Purchase #6	$45.90	11.250%	$51.0638	$51.06	$51.05	$51.10
Purchase #7	$115.63	4.185%	$120.4691	$120.47	$120.45	$120.50
7 purchase totals =	$822.51		$902.3610	$902.36	$902.30	$902.50