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	$73.30	9.550%	$80.3002	$80.30	$80.30	$80.30
Purchase #2	$159.59	7.705%	$171.8864	$171.89	$171.90	$171.90
Purchase #3	$219.89	4.496%	$229.7763	$229.78	$229.80	$229.80
Purchase #4	$58.73	4.418%	$61.3247	$61.32	$61.30	$61.30
Purchase #5	$217.81	8.438%	$236.1888	$236.19	$236.20	$236.20
Purchase #6	$40.34	5.354%	$42.4998	$42.50	$42.50	$42.50
Purchase #7	$6.91	13.415%	$7.837	$7.84	$7.85	$7.80
7 purchase totals =	$776.57		$829.8132	$829.82	$829.85	$829.80