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	$239.61	13.324%	$271.5356	$271.54	$271.55	$271.50
Purchase #2	$69.31	4.532%	$72.4511	$72.45	$72.45	$72.50
Purchase #3	$162.50	12.280%	$182.455	$182.46	$182.45	$182.50
Purchase #4	$181.64	7.362%	$195.0123	$195.01	$195.00	$195.00
Purchase #5	$242.58	10.678%	$268.4827	$268.48	$268.50	$268.50
Purchase #6	$55.90	5.158%	$58.7833	$58.78	$58.80	$58.80
Purchase #7	$37.91	12.461%	$42.634	$42.63	$42.65	$42.60
7 purchase totals =	$989.45		$1,091.3540	$1,091.35	$1,091.40	$1,091.40