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 $211.90   13.749%   $241.0341   $241.03   $241.05   $241.00  
  Purchase #2 $127.43   12.534%   $143.4021   $143.40   $143.40   $143.40  
  Purchase #3 $178.89   8.332%   $193.7951   $193.80   $193.80   $193.80  
  Purchase #4 $163.48   11.865%   $182.8769   $182.88   $182.90   $182.90  
  Purchase #5 $115.59   4.439%   $120.721   $120.72   $120.70   $120.70  
  Purchase #6 $29.93   4.145%   $31.1706   $31.17   $31.15   $31.20  
  Purchase #7 $56.66   5.290%   $59.6573   $59.66   $59.65   $59.70  
  7 purchase totals = $883.88       $972.6571   $972.66   $972.65   $972.70