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	$131.27	6.538%	$139.8524	$139.85	$139.85	$139.90
Purchase #2	$76.40	12.266%	$85.7712	$85.77	$85.75	$85.80
Purchase #3	$44.61	13.867%	$50.7961	$50.80	$50.80	$50.80
Purchase #4	$209.72	5.867%	$222.0243	$222.02	$222.00	$222.00
Purchase #5	$125.89	3.232%	$129.9588	$129.96	$129.95	$130.00
Purchase #6	$150.64	10.364%	$166.2523	$166.25	$166.25	$166.30
Purchase #7	$210.46	7.220%	$225.6552	$225.66	$225.65	$225.70
7 purchase totals =	$948.99		$1,020.3103	$1,020.31	$1,020.25	$1,020.50