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	$230.38	8.442%	$249.8287	$249.83	$249.85	$249.80
Purchase #2	$104.36	10.424%	$115.2385	$115.24	$115.25	$115.20
Purchase #3	$72.73	7.223%	$77.9833	$77.98	$78.00	$78.00
Purchase #4	$18.62	12.115%	$20.8758	$20.88	$20.90	$20.90
Purchase #5	$224.59	13.333%	$254.5346	$254.53	$254.55	$254.50
Purchase #6	$152.86	12.428%	$171.8574	$171.86	$171.85	$171.90
Purchase #7	$240.99	11.848%	$269.5425	$269.54	$269.55	$269.50
7 purchase totals =	$1,044.53		$1,159.8608	$1,159.86	$1,159.95	$1,159.80