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	$80.26	13.415%	$91.0269	$91.03	$91.05	$91.00
Purchase #2	$217.52	11.739%	$243.0547	$243.05	$243.05	$243.10
Purchase #3	$191.73	13.399%	$217.4199	$217.42	$217.40	$217.40
Purchase #4	$43.54	9.121%	$47.5113	$47.51	$47.50	$47.50
Purchase #5	$166.71	7.677%	$179.5083	$179.51	$179.50	$179.50
Purchase #6	$127.61	9.362%	$139.5568	$139.56	$139.55	$139.60
Purchase #7	$35.60	13.294%	$40.3327	$40.33	$40.35	$40.30
7 purchase totals =	$862.97		$958.4106	$958.41	$958.40	$958.40