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	$128.33	11.217%	$142.7248	$142.72	$142.70	$142.70
Purchase #2	$227.32	5.678%	$240.2272	$240.23	$240.25	$240.20
Purchase #3	$28.75	7.456%	$30.8936	$30.89	$30.90	$30.90
Purchase #4	$157.33	9.483%	$172.2496	$172.25	$172.25	$172.20
Purchase #5	$89.98	10.430%	$99.3649	$99.36	$99.35	$99.40
Purchase #6	$221.51	12.809%	$249.8832	$249.88	$249.90	$249.90
Purchase #7	$88.48	7.274%	$94.916	$94.92	$94.90	$94.90
7 purchase totals =	$941.70		$1,030.2593	$1,030.25	$1,030.25	$1,030.20