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	$68.53	7.270%	$73.5121	$73.51	$73.50	$73.50
Purchase #2	$100.75	8.598%	$109.4125	$109.41	$109.40	$109.40
Purchase #3	$171.66	7.196%	$184.0127	$184.01	$184.00	$184.00
Purchase #4	$31.38	12.512%	$35.3063	$35.31	$35.30	$35.30
Purchase #5	$79.27	3.604%	$82.1269	$82.13	$82.15	$82.10
Purchase #6	$175.97	12.522%	$198.005	$198.01	$198.00	$198.00
Purchase #7	$181.57	10.555%	$200.7347	$200.73	$200.75	$200.70
7 purchase totals =	$809.13		$883.1102	$883.11	$883.10	$883.00