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	$115.37	11.134%	$128.2153	$128.22	$128.20	$128.20
Purchase #2	$235.64	8.721%	$256.1902	$256.19	$256.20	$256.20
Purchase #3	$100.32	6.190%	$106.5298	$106.53	$106.55	$106.50
Purchase #4	$107.98	7.676%	$116.2685	$116.27	$116.25	$116.30
Purchase #5	$135.78	9.562%	$148.7633	$148.76	$148.75	$148.80
Purchase #6	$190.30	3.484%	$196.9301	$196.93	$196.95	$196.90
Purchase #7	$117.71	4.720%	$123.2659	$123.27	$123.25	$123.30
7 purchase totals =	$1,003.10		$1,076.1631	$1,076.17	$1,076.15	$1,076.20