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	$113.47	12.774%	$127.9647	$127.96	$127.95	$128.00
Purchase #2	$191.69	9.357%	$209.6264	$209.63	$209.65	$209.60
Purchase #3	$63.51	13.726%	$72.2274	$72.23	$72.25	$72.20
Purchase #4	$55.44	7.434%	$59.5614	$59.56	$59.55	$59.60
Purchase #5	$79.26	9.665%	$86.9205	$86.92	$86.90	$86.90
Purchase #6	$233.98	8.483%	$253.8285	$253.83	$253.85	$253.80
Purchase #7	$73.86	12.263%	$82.9175	$82.92	$82.90	$82.90
7 purchase totals =	$811.21		$893.0464	$893.05	$893.05	$893.00