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	$6.31	13.462%	$7.1595	$7.16	$7.15	$7.20
Purchase #2	$217.48	10.303%	$239.887	$239.89	$239.90	$239.90
Purchase #3	$82.38	12.279%	$92.4954	$92.50	$92.50	$92.50
Purchase #4	$125.31	7.872%	$135.1744	$135.17	$135.15	$135.20
Purchase #5	$29.46	7.339%	$31.6221	$31.62	$31.60	$31.60
Purchase #6	$217.37	3.869%	$225.78	$225.78	$225.80	$225.80
Purchase #7	$54.74	13.801%	$62.2947	$62.29	$62.30	$62.30
7 purchase totals =	$733.05		$794.4131	$794.41	$794.40	$794.50