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	$122.47	13.718%	$139.2704	$139.27	$139.25	$139.30
Purchase #2	$151.54	11.424%	$168.8519	$168.85	$168.85	$168.90
Purchase #3	$52.76	12.111%	$59.1498	$59.15	$59.15	$59.10
Purchase #4	$133.69	3.310%	$138.1151	$138.12	$138.10	$138.10
Purchase #5	$195.60	6.499%	$208.312	$208.31	$208.30	$208.30
Purchase #6	$210.72	6.555%	$224.5327	$224.53	$224.55	$224.50
Purchase #7	$58.73	11.232%	$65.3266	$65.33	$65.35	$65.30
7 purchase totals =	$925.51		$1,003.5585	$1,003.56	$1,003.55	$1,003.50