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	$98.89	10.347%	$109.1221	$109.12	$109.10	$109.10
Purchase #2	$44.66	6.467%	$47.5482	$47.55	$47.55	$47.50
Purchase #3	$97.86	3.612%	$101.3947	$101.39	$101.40	$101.40
Purchase #4	$47.88	7.635%	$51.5356	$51.54	$51.55	$51.50
Purchase #5	$152.77	10.136%	$168.2548	$168.25	$168.25	$168.30
Purchase #6	$89.75	12.715%	$101.1617	$101.16	$101.15	$101.20
Purchase #7	$237.88	4.843%	$249.4005	$249.40	$249.40	$249.40
7 purchase totals =	$769.69		$828.4176	$828.41	$828.40	$828.40