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	$199.26	9.513%	$218.2156	$218.22	$218.20	$218.20
Purchase #2	$215.76	9.265%	$235.7502	$235.75	$235.75	$235.80
Purchase #3	$154.96	10.496%	$171.2246	$171.22	$171.20	$171.20
Purchase #4	$164.78	9.796%	$180.9218	$180.92	$180.90	$180.90
Purchase #5	$101.56	3.402%	$105.0151	$105.02	$105.00	$105.00
Purchase #6	$31.57	4.522%	$32.9976	$33.00	$33.00	$33.00
Purchase #7	$55.28	4.722%	$57.8903	$57.89	$57.90	$57.90
7 purchase totals =	$923.17		$1,002.0152	$1,002.02	$1,001.95	$1,002.00