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	$73.82	7.742%	$79.5351	$79.54	$79.55	$79.50
Purchase #2	$39.46	9.453%	$43.1902	$43.19	$43.20	$43.20
Purchase #3	$29.98	10.516%	$33.1327	$33.13	$33.15	$33.10
Purchase #4	$79.57	8.398%	$86.2523	$86.25	$86.25	$86.30
Purchase #5	$177.61	7.792%	$191.4494	$191.45	$191.45	$191.40
Purchase #6	$57.33	12.392%	$64.4343	$64.43	$64.45	$64.40
Purchase #7	$58.30	8.818%	$63.4409	$63.44	$63.45	$63.40
7 purchase totals =	$516.07		$561.4349	$561.43	$561.50	$561.30