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	$88.38	12.339%	$99.2852	$99.29	$99.30	$99.30
Purchase #2	$202.86	9.332%	$221.7909	$221.79	$221.80	$221.80
Purchase #3	$148.76	8.668%	$161.6545	$161.65	$161.65	$161.70
Purchase #4	$150.56	7.651%	$162.0793	$162.08	$162.10	$162.10
Purchase #5	$244.92	7.743%	$263.8842	$263.88	$263.90	$263.90
Purchase #6	$189.96	13.206%	$215.0461	$215.05	$215.05	$215.00
Purchase #7	$67.92	7.266%	$72.8551	$72.86	$72.85	$72.90
7 purchase totals =	$1,093.36		$1,196.5953	$1,196.60	$1,196.65	$1,196.70