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	$39.53	6.365%	$42.0461	$42.05	$42.05	$42.00
Purchase #2	$228.68	13.214%	$258.8978	$258.90	$258.90	$258.90
Purchase #3	$229.67	5.780%	$242.9449	$242.94	$242.95	$242.90
Purchase #4	$212.48	3.157%	$219.188	$219.19	$219.20	$219.20
Purchase #5	$45.72	11.288%	$50.8809	$50.88	$50.90	$50.90
Purchase #6	$59.67	4.630%	$62.4327	$62.43	$62.45	$62.40
Purchase #7	$125.38	11.137%	$139.3436	$139.34	$139.35	$139.30
7 purchase totals =	$941.13		$1,015.7340	$1,015.73	$1,015.80	$1,015.60