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	$173.42	9.299%	$189.5463	$189.55	$189.55	$189.50
Purchase #2	$99.98	9.843%	$109.821	$109.82	$109.80	$109.80
Purchase #3	$196.42	6.803%	$209.7825	$209.78	$209.80	$209.80
Purchase #4	$36.64	6.383%	$38.9787	$38.98	$39.00	$39.00
Purchase #5	$152.96	9.790%	$167.9348	$167.93	$167.95	$167.90
Purchase #6	$73.87	8.563%	$80.1955	$80.20	$80.20	$80.20
Purchase #7	$224.80	11.493%	$250.6363	$250.64	$250.65	$250.60
7 purchase totals =	$958.09		$1,046.8951	$1,046.90	$1,046.95	$1,046.80