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	$198.26	13.139%	$224.3094	$224.31	$224.30	$224.30
Purchase #2	$58.33	5.254%	$61.3947	$61.39	$61.40	$61.40
Purchase #3	$245.82	5.324%	$258.9075	$258.91	$258.90	$258.90
Purchase #4	$136.34	8.689%	$148.1866	$148.19	$148.20	$148.20
Purchase #5	$134.54	6.684%	$143.5327	$143.53	$143.55	$143.50
Purchase #6	$72.34	8.253%	$78.3102	$78.31	$78.30	$78.30
Purchase #7	$80.73	4.826%	$84.626	$84.63	$84.65	$84.60
7 purchase totals =	$926.36		$999.2671	$999.27	$999.30	$999.20