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	$74.71	10.410%	$82.4873	$82.49	$82.50	$82.50
Purchase #2	$131.40	9.368%	$143.7096	$143.71	$143.70	$143.70
Purchase #3	$18.44	10.119%	$20.3059	$20.31	$20.30	$20.30
Purchase #4	$124.44	9.494%	$136.2543	$136.25	$136.25	$136.30
Purchase #5	$28.96	10.425%	$31.9791	$31.98	$32.00	$32.00
Purchase #6	$189.46	7.511%	$203.6903	$203.69	$203.70	$203.70
Purchase #7	$41.56	8.565%	$45.1196	$45.12	$45.10	$45.10
7 purchase totals =	$608.97		$663.5461	$663.55	$663.55	$663.60