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	$176.90	3.700%	$183.4453	$183.45	$183.45	$183.40
Purchase #2	$93.69	6.382%	$99.6693	$99.67	$99.65	$99.70
Purchase #3	$245.59	10.270%	$270.8121	$270.81	$270.80	$270.80
Purchase #4	$85.89	4.809%	$90.0205	$90.02	$90.00	$90.00
Purchase #5	$223.65	8.582%	$242.8436	$242.84	$242.85	$242.80
Purchase #6	$59.91	4.245%	$62.4532	$62.45	$62.45	$62.50
Purchase #7	$51.79	8.345%	$56.1119	$56.11	$56.10	$56.10
7 purchase totals =	$937.42		$1,005.3559	$1,005.35	$1,005.30	$1,005.30