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	$83.31	8.497%	$90.3889	$90.39	$90.40	$90.40
Purchase #2	$78.27	4.740%	$81.98	$81.98	$82.00	$82.00
Purchase #3	$180.77	7.561%	$194.438	$194.44	$194.45	$194.40
Purchase #4	$9.48	9.429%	$10.3739	$10.37	$10.35	$10.40
Purchase #5	$78.82	6.796%	$84.1766	$84.18	$84.20	$84.20
Purchase #6	$188.33	9.814%	$206.8127	$206.81	$206.80	$206.80
Purchase #7	$89.83	10.614%	$99.3646	$99.36	$99.35	$99.40
7 purchase totals =	$708.81		$767.5347	$767.53	$767.55	$767.60