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	$120.78	8.371%	$130.8905	$130.89	$130.90	$130.90
Purchase #2	$240.33	7.487%	$258.3235	$258.32	$258.30	$258.30
Purchase #3	$86.57	3.771%	$89.8346	$89.83	$89.85	$89.80
Purchase #4	$7.93	9.790%	$8.7063	$8.71	$8.70	$8.70
Purchase #5	$73.61	13.493%	$83.5422	$83.54	$83.55	$83.50
Purchase #6	$181.76	12.139%	$203.8238	$203.82	$203.80	$203.80
Purchase #7	$233.91	7.269%	$250.9129	$250.91	$250.90	$250.90
7 purchase totals =	$944.89		$1,026.0338	$1,026.02	$1,026.00	$1,025.90