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	$128.38	8.539%	$139.3424	$139.34	$139.35	$139.30
Purchase #2	$38.40	11.575%	$42.8448	$42.84	$42.85	$42.80
Purchase #3	$85.37	8.516%	$92.6401	$92.64	$92.65	$92.60
Purchase #4	$223.62	7.711%	$240.8633	$240.86	$240.85	$240.90
Purchase #5	$93.71	13.347%	$106.2175	$106.22	$106.20	$106.20
Purchase #6	$42.81	6.575%	$45.6248	$45.62	$45.60	$45.60
Purchase #7	$79.84	4.819%	$83.6875	$83.69	$83.70	$83.70
7 purchase totals =	$692.13		$751.2204	$751.21	$751.20	$751.10