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	$40.55	3.284%	$41.8817	$41.88	$41.90	$41.90
Purchase #2	$59.97	11.236%	$66.7082	$66.71	$66.70	$66.70
Purchase #3	$31.35	5.629%	$33.1147	$33.11	$33.10	$33.10
Purchase #4	$169.90	9.369%	$185.8179	$185.82	$185.80	$185.80
Purchase #5	$28.33	11.642%	$31.6282	$31.63	$31.65	$31.60
Purchase #6	$209.25	5.265%	$220.267	$220.27	$220.25	$220.30
Purchase #7	$210.71	8.700%	$229.0418	$229.04	$229.05	$229.00
7 purchase totals =	$750.06		$808.4595	$808.46	$808.45	$808.40