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	$78.75	5.280%	$82.908	$82.91	$82.90	$82.90
Purchase #2	$144.38	7.460%	$155.1507	$155.15	$155.15	$155.20
Purchase #3	$234.78	5.771%	$248.3292	$248.33	$248.35	$248.30
Purchase #4	$80.36	11.455%	$89.5652	$89.57	$89.55	$89.60
Purchase #5	$236.31	10.758%	$261.7322	$261.73	$261.75	$261.70
Purchase #6	$72.70	5.567%	$76.7472	$76.75	$76.75	$76.70
Purchase #7	$50.59	7.349%	$54.3079	$54.31	$54.30	$54.30
7 purchase totals =	$897.87		$968.7404	$968.75	$968.75	$968.70