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	$156.50	6.107%	$166.0575	$166.06	$166.05	$166.10
Purchase #2	$203.70	3.553%	$210.9375	$210.94	$210.95	$210.90
Purchase #3	$216.39	12.719%	$243.9126	$243.91	$243.90	$243.90
Purchase #4	$72.46	8.601%	$78.6923	$78.69	$78.70	$78.70
Purchase #5	$73.31	9.633%	$80.372	$80.37	$80.35	$80.40
Purchase #6	$40.63	3.158%	$41.9131	$41.91	$41.90	$41.90
Purchase #7	$79.95	3.785%	$82.9761	$82.98	$83.00	$83.00
7 purchase totals =	$842.94		$904.8611	$904.86	$904.85	$904.90