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	$106.72	3.444%	$110.3954	$110.40	$110.40	$110.40
Purchase #2	$215.48	9.273%	$235.4615	$235.46	$235.45	$235.50
Purchase #3	$41.32	4.355%	$43.1195	$43.12	$43.10	$43.10
Purchase #4	$82.47	8.560%	$89.5294	$89.53	$89.55	$89.50
Purchase #5	$110.41	5.714%	$116.7188	$116.72	$116.70	$116.70
Purchase #6	$162.84	12.277%	$182.8319	$182.83	$182.85	$182.80
Purchase #7	$165.31	8.781%	$179.8259	$179.83	$179.85	$179.80
7 purchase totals =	$884.55		$957.8824	$957.89	$957.90	$957.80