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	$198.87	3.815%	$206.4569	$206.46	$206.45	$206.50
Purchase #2	$65.94	4.822%	$69.1196	$69.12	$69.10	$69.10
Purchase #3	$86.90	4.639%	$90.9313	$90.93	$90.95	$90.90
Purchase #4	$198.27	7.484%	$213.1085	$213.11	$213.10	$213.10
Purchase #5	$229.32	9.306%	$250.6605	$250.66	$250.65	$250.70
Purchase #6	$69.46	10.117%	$76.4873	$76.49	$76.50	$76.50
Purchase #7	$67.28	7.712%	$72.4686	$72.47	$72.45	$72.50
7 purchase totals =	$916.04		$979.2327	$979.24	$979.20	$979.30