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	$84.93	5.280%	$89.4143	$89.41	$89.40	$89.40
Purchase #2	$157.30	9.298%	$171.9258	$171.93	$171.95	$171.90
Purchase #3	$41.62	5.820%	$44.0423	$44.04	$44.05	$44.00
Purchase #4	$84.45	11.398%	$94.0756	$94.08	$94.10	$94.10
Purchase #5	$70.94	12.123%	$79.5401	$79.54	$79.55	$79.50
Purchase #6	$178.69	5.362%	$188.2714	$188.27	$188.25	$188.30
Purchase #7	$81.72	4.860%	$85.6916	$85.69	$85.70	$85.70
7 purchase totals =	$699.65		$752.9611	$752.96	$753.00	$752.90