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	$202.48	9.818%	$222.3595	$222.36	$222.35	$222.40
Purchase #2	$200.87	12.417%	$225.812	$225.81	$225.80	$225.80
Purchase #3	$213.73	3.157%	$220.4775	$220.48	$220.50	$220.50
Purchase #4	$105.57	3.731%	$109.5088	$109.51	$109.50	$109.50
Purchase #5	$73.37	11.619%	$81.8949	$81.89	$81.90	$81.90
Purchase #6	$228.26	9.316%	$249.5247	$249.52	$249.50	$249.50
Purchase #7	$211.55	5.674%	$223.5533	$223.55	$223.55	$223.60
7 purchase totals =	$1,235.83		$1,333.1307	$1,333.12	$1,333.10	$1,333.20