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 $92.59   4.325%   $96.5945   $96.59   $96.60   $96.60  
  Purchase #2 $213.59   11.445%   $238.0354   $238.04   $238.05   $238.00  
  Purchase #3 $227.75   7.295%   $244.3644   $244.36   $244.35   $244.40  
  Purchase #4 $24.75   12.760%   $27.9081   $27.91   $27.90   $27.90  
  Purchase #5 $194.29   6.333%   $206.5944   $206.59   $206.60   $206.60  
  Purchase #6 $156.70   13.159%   $177.3202   $177.32   $177.30   $177.30  
  Purchase #7 $5.41   8.782%   $5.8851   $5.89   $5.90   $5.90  
  7 purchase totals = $915.08       $996.7021   $996.70   $996.70   $996.70