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	$149.97	6.254%	$159.3491	$159.35	$159.35	$159.30
Purchase #2	$68.46	7.807%	$73.8047	$73.80	$73.80	$73.80
Purchase #3	$56.76	5.213%	$59.7189	$59.72	$59.70	$59.70
Purchase #4	$57.74	6.213%	$61.3274	$61.33	$61.35	$61.30
Purchase #5	$211.83	5.394%	$223.2561	$223.26	$223.25	$223.30
Purchase #6	$109.39	9.507%	$119.7897	$119.79	$119.80	$119.80
Purchase #7	$140.37	11.765%	$156.8845	$156.88	$156.90	$156.90
7 purchase totals =	$794.52		$854.1304	$854.13	$854.15	$854.10