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	$83.84	6.229%	$89.0624	$89.06	$89.05	$89.10
Purchase #2	$179.56	3.363%	$185.5986	$185.60	$185.60	$185.60
Purchase #3	$36.82	3.330%	$38.0461	$38.05	$38.05	$38.00
Purchase #4	$181.48	7.216%	$194.5756	$194.58	$194.60	$194.60
Purchase #5	$219.87	8.511%	$238.5831	$238.58	$238.60	$238.60
Purchase #6	$249.27	7.680%	$268.4139	$268.41	$268.40	$268.40
Purchase #7	$113.49	3.183%	$117.1024	$117.10	$117.10	$117.10
7 purchase totals =	$1,064.33		$1,131.3821	$1,131.38	$1,131.40	$1,131.40