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	$97.31	7.170%	$104.2871	$104.29	$104.30	$104.30
Purchase #2	$65.95	9.797%	$72.4111	$72.41	$72.40	$72.40
Purchase #3	$108.55	3.799%	$112.6738	$112.67	$112.65	$112.70
Purchase #4	$62.35	11.151%	$69.3026	$69.30	$69.30	$69.30
Purchase #5	$239.98	4.491%	$250.7575	$250.76	$250.75	$250.80
Purchase #6	$155.47	4.410%	$162.3262	$162.33	$162.35	$162.30
Purchase #7	$79.72	4.786%	$83.5354	$83.54	$83.55	$83.50
7 purchase totals =	$809.33		$855.2937	$855.30	$855.30	$855.30