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	$142.61	9.410%	$156.0296	$156.03	$156.05	$156.00
Purchase #2	$72.54	11.250%	$80.7008	$80.70	$80.70	$80.70
Purchase #3	$80.47	11.805%	$89.9695	$89.97	$89.95	$90.00
Purchase #4	$65.51	11.538%	$73.0685	$73.07	$73.05	$73.10
Purchase #5	$101.91	8.761%	$110.8383	$110.84	$110.85	$110.80
Purchase #6	$98.36	11.551%	$109.7216	$109.72	$109.70	$109.70
Purchase #7	$189.77	5.238%	$199.7102	$199.71	$199.70	$199.70
7 purchase totals =	$751.17		$820.0385	$820.04	$820.00	$820.00