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	$31.99	3.588%	$33.1378	$33.14	$33.15	$33.10
Purchase #2	$203.31	9.599%	$222.8257	$222.83	$222.85	$222.80
Purchase #3	$78.45	10.670%	$86.8206	$86.82	$86.80	$86.80
Purchase #4	$84.48	11.654%	$94.3253	$94.33	$94.35	$94.30
Purchase #5	$39.26	13.452%	$44.5413	$44.54	$44.55	$44.50
Purchase #6	$171.48	9.113%	$187.107	$187.11	$187.10	$187.10
Purchase #7	$18.41	11.675%	$20.5594	$20.56	$20.55	$20.60
7 purchase totals =	$627.38		$689.3171	$689.33	$689.35	$689.20