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	$141.49	3.346%	$146.2243	$146.22	$146.20	$146.20
Purchase #2	$83.69	6.164%	$88.8487	$88.85	$88.85	$88.80
Purchase #3	$98.50	7.806%	$106.1889	$106.19	$106.20	$106.20
Purchase #4	$38.99	3.560%	$40.378	$40.38	$40.40	$40.40
Purchase #5	$67.99	6.716%	$72.5562	$72.56	$72.55	$72.60
Purchase #6	$200.98	7.199%	$215.4486	$215.45	$215.45	$215.40
Purchase #7	$136.81	7.677%	$147.3129	$147.31	$147.30	$147.30
7 purchase totals =	$768.45		$816.9576	$816.96	$816.95	$816.90