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	$79.63	3.534%	$82.4441	$82.44	$82.45	$82.40
Purchase #2	$220.42	12.666%	$248.3384	$248.34	$248.35	$248.30
Purchase #3	$167.71	8.720%	$182.3343	$182.33	$182.35	$182.30
Purchase #4	$40.96	3.377%	$42.3432	$42.34	$42.35	$42.30
Purchase #5	$129.31	3.841%	$134.2768	$134.28	$134.30	$134.30
Purchase #6	$83.55	8.602%	$90.737	$90.74	$90.75	$90.70
Purchase #7	$71.81	12.560%	$80.8293	$80.83	$80.85	$80.80
7 purchase totals =	$793.39		$861.3031	$861.30	$861.40	$861.10