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	$37.90	8.202%	$41.0086	$41.01	$41.00	$41.00
Purchase #2	$18.64	7.868%	$20.1066	$20.11	$20.10	$20.10
Purchase #3	$98.47	12.270%	$110.5523	$110.55	$110.55	$110.60
Purchase #4	$193.44	7.536%	$208.0176	$208.02	$208.00	$208.00
Purchase #5	$229.78	11.475%	$256.1473	$256.15	$256.15	$256.10
Purchase #6	$30.62	7.713%	$32.9817	$32.98	$33.00	$33.00
Purchase #7	$78.59	13.705%	$89.3608	$89.36	$89.35	$89.40
7 purchase totals =	$687.44		$758.1749	$758.18	$758.15	$758.20