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	$237.88	6.530%	$253.4136	$253.41	$253.40	$253.40
Purchase #2	$242.66	3.168%	$250.3475	$250.35	$250.35	$250.30
Purchase #3	$196.62	12.165%	$220.5388	$220.54	$220.55	$220.50
Purchase #4	$141.47	6.301%	$150.384	$150.38	$150.40	$150.40
Purchase #5	$26.41	4.409%	$27.5744	$27.57	$27.55	$27.60
Purchase #6	$38.68	4.353%	$40.3637	$40.36	$40.35	$40.40
Purchase #7	$93.39	7.135%	$100.0534	$100.05	$100.05	$100.10
7 purchase totals =	$977.11		$1,042.6754	$1,042.66	$1,042.65	$1,042.70