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	$28.33	10.810%	$31.3925	$31.39	$31.40	$31.40
Purchase #2	$203.70	9.607%	$223.2695	$223.27	$223.25	$223.30
Purchase #3	$218.42	4.546%	$228.3494	$228.35	$228.35	$228.30
Purchase #4	$55.64	11.625%	$62.1082	$62.11	$62.10	$62.10
Purchase #5	$190.42	12.150%	$213.556	$213.56	$213.55	$213.60
Purchase #6	$196.79	7.709%	$211.9605	$211.96	$211.95	$212.00
Purchase #7	$31.56	5.688%	$33.3551	$33.36	$33.35	$33.40
7 purchase totals =	$924.86		$1,003.9912	$1,004.00	$1,003.95	$1,004.10