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	$93.80	7.327%	$100.6727	$100.67	$100.65	$100.70
Purchase #2	$200.59	9.148%	$218.94	$218.94	$218.95	$218.90
Purchase #3	$36.44	13.192%	$41.2472	$41.25	$41.25	$41.20
Purchase #4	$84.67	6.122%	$89.8535	$89.85	$89.85	$89.90
Purchase #5	$97.89	6.774%	$104.5211	$104.52	$104.50	$104.50
Purchase #6	$37.26	5.241%	$39.2128	$39.21	$39.20	$39.20
Purchase #7	$119.86	12.837%	$135.2464	$135.25	$135.25	$135.20
7 purchase totals =	$670.51		$729.6937	$729.69	$729.65	$729.60