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	$15.40	4.618%	$16.1112	$16.11	$16.10	$16.10
Purchase #2	$106.66	4.609%	$111.576	$111.58	$111.60	$111.60
Purchase #3	$130.27	9.291%	$142.3734	$142.37	$142.35	$142.40
Purchase #4	$233.84	4.145%	$243.5327	$243.53	$243.55	$243.50
Purchase #5	$84.71	9.340%	$92.6219	$92.62	$92.60	$92.60
Purchase #6	$89.69	9.844%	$98.5191	$98.52	$98.50	$98.50
Purchase #7	$189.86	12.243%	$213.1046	$213.10	$213.10	$213.10
7 purchase totals =	$850.43		$917.8389	$917.83	$917.80	$917.80