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	$82.96	10.638%	$91.7853	$91.79	$91.80	$91.80
Purchase #2	$213.36	12.702%	$240.461	$240.46	$240.45	$240.50
Purchase #3	$91.64	7.474%	$98.4892	$98.49	$98.50	$98.50
Purchase #4	$97.80	6.689%	$104.3418	$104.34	$104.35	$104.30
Purchase #5	$33.37	11.837%	$37.32	$37.32	$37.30	$37.30
Purchase #6	$93.93	3.582%	$97.2946	$97.29	$97.30	$97.30
Purchase #7	$117.43	11.651%	$131.1118	$131.11	$131.10	$131.10
7 purchase totals =	$730.49		$800.8037	$800.80	$800.80	$800.80