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	$76.36	3.625%	$79.1281	$79.13	$79.15	$79.10
Purchase #2	$47.51	9.849%	$52.1893	$52.19	$52.20	$52.20
Purchase #3	$153.29	7.610%	$164.9554	$164.96	$164.95	$165.00
Purchase #4	$30.86	3.269%	$31.8688	$31.87	$31.85	$31.90
Purchase #5	$47.53	13.298%	$53.8505	$53.85	$53.85	$53.90
Purchase #6	$34.71	9.148%	$37.8853	$37.89	$37.90	$37.90
Purchase #7	$221.46	12.793%	$249.7914	$249.79	$249.80	$249.80
7 purchase totals =	$611.72		$669.6688	$669.68	$669.70	$669.80