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	$29.48	12.314%	$33.1102	$33.11	$33.10	$33.10
Purchase #2	$211.82	7.704%	$228.1386	$228.14	$228.15	$228.10
Purchase #3	$211.58	5.506%	$223.2296	$223.23	$223.25	$223.20
Purchase #4	$155.50	8.290%	$168.391	$168.39	$168.40	$168.40
Purchase #5	$167.72	13.583%	$190.5014	$190.50	$190.50	$190.50
Purchase #6	$123.55	5.109%	$129.8622	$129.86	$129.85	$129.90
Purchase #7	$112.80	6.362%	$119.9763	$119.98	$120.00	$120.00
7 purchase totals =	$1,012.45		$1,093.2093	$1,093.21	$1,093.25	$1,093.20