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	$206.50	4.786%	$216.3831	$216.38	$216.40	$216.40
Purchase #2	$83.41	12.213%	$93.5969	$93.60	$93.60	$93.60
Purchase #3	$84.90	10.221%	$93.5776	$93.58	$93.60	$93.60
Purchase #4	$247.31	11.440%	$275.6023	$275.60	$275.60	$275.60
Purchase #5	$167.84	10.543%	$185.5354	$185.54	$185.55	$185.50
Purchase #6	$26.34	6.343%	$28.0107	$28.01	$28.00	$28.00
Purchase #7	$31.64	6.661%	$33.7475	$33.75	$33.75	$33.70
7 purchase totals =	$847.94		$926.4535	$926.46	$926.50	$926.40