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	$99.87	4.682%	$104.5459	$104.55	$104.55	$104.50
Purchase #2	$56.57	8.728%	$61.5074	$61.51	$61.50	$61.50
Purchase #3	$27.30	3.544%	$28.2675	$28.27	$28.25	$28.30
Purchase #4	$79.97	11.336%	$89.0354	$89.04	$89.05	$89.00
Purchase #5	$68.88	4.552%	$72.0154	$72.02	$72.00	$72.00
Purchase #6	$112.60	8.423%	$122.0843	$122.08	$122.10	$122.10
Purchase #7	$22.57	12.743%	$25.4461	$25.45	$25.45	$25.40
7 purchase totals =	$467.76		$502.9020	$502.92	$502.90	$502.80