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	$126.74	6.570%	$135.0668	$135.07	$135.05	$135.10
Purchase #2	$165.72	10.349%	$182.8704	$182.87	$182.85	$182.90
Purchase #3	$131.67	6.215%	$139.8533	$139.85	$139.85	$139.90
Purchase #4	$242.27	6.630%	$258.3325	$258.33	$258.35	$258.30
Purchase #5	$213.63	7.243%	$229.1032	$229.10	$229.10	$229.10
Purchase #6	$38.68	9.592%	$42.3902	$42.39	$42.40	$42.40
Purchase #7	$158.72	6.166%	$168.5067	$168.51	$168.50	$168.50
7 purchase totals =	$1,077.43		$1,156.1231	$1,156.12	$1,156.10	$1,156.20