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	$44.77	11.782%	$50.0448	$50.04	$50.05	$50.00
Purchase #2	$152.34	11.815%	$170.339	$170.34	$170.35	$170.30
Purchase #3	$213.63	3.640%	$221.4061	$221.41	$221.40	$221.40
Purchase #4	$62.86	13.120%	$71.1072	$71.11	$71.10	$71.10
Purchase #5	$171.33	10.620%	$189.5252	$189.53	$189.55	$189.50
Purchase #6	$220.50	9.812%	$242.1355	$242.14	$242.15	$242.10
Purchase #7	$136.84	3.684%	$141.8812	$141.88	$141.90	$141.90
7 purchase totals =	$1,002.27		$1,086.4390	$1,086.45	$1,086.50	$1,086.30