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	$159.30	13.133%	$180.2209	$180.22	$180.20	$180.20
Purchase #2	$219.78	13.674%	$249.8327	$249.83	$249.85	$249.80
Purchase #3	$59.93	12.399%	$67.3607	$67.36	$67.35	$67.40
Purchase #4	$97.90	6.870%	$104.6257	$104.63	$104.65	$104.60
Purchase #5	$166.57	11.115%	$185.0843	$185.08	$185.10	$185.10
Purchase #6	$40.43	11.498%	$45.0786	$45.08	$45.10	$45.10
Purchase #7	$24.46	11.646%	$27.3086	$27.31	$27.30	$27.30
7 purchase totals =	$768.37		$859.5115	$859.51	$859.55	$859.50