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	$155.81	6.235%	$165.5248	$165.52	$165.50	$165.50
Purchase #2	$89.71	6.800%	$95.8103	$95.81	$95.80	$95.80
Purchase #3	$217.57	11.372%	$242.3121	$242.31	$242.30	$242.30
Purchase #4	$191.40	11.470%	$213.3536	$213.35	$213.35	$213.40
Purchase #5	$222.47	4.380%	$232.2142	$232.21	$232.20	$232.20
Purchase #6	$11.37	13.828%	$12.9422	$12.94	$12.95	$12.90
Purchase #7	$171.74	7.833%	$185.1924	$185.19	$185.20	$185.20
7 purchase totals =	$1,060.07		$1,147.3496	$1,147.33	$1,147.30	$1,147.30