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	$41.90	5.572%	$44.2347	$44.23	$44.25	$44.20
Purchase #2	$144.35	9.761%	$158.44	$158.44	$158.45	$158.40
Purchase #3	$127.81	10.227%	$140.8811	$140.88	$140.90	$140.90
Purchase #4	$223.61	10.582%	$247.2724	$247.27	$247.25	$247.30
Purchase #5	$136.91	3.650%	$141.9072	$141.91	$141.90	$141.90
Purchase #6	$35.84	4.780%	$37.5532	$37.55	$37.55	$37.60
Purchase #7	$78.71	9.780%	$86.4078	$86.41	$86.40	$86.40
7 purchase totals =	$789.13		$856.6964	$856.69	$856.70	$856.70