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 $113.93   5.764%   $120.4969   $120.50   $120.50   $120.50  
  Purchase #2 $157.95   9.269%   $172.5904   $172.59   $172.60   $172.60  
  Purchase #3 $78.55   10.353%   $86.6823   $86.68   $86.70   $86.70  
  Purchase #4 $232.25   4.839%   $243.4886   $243.49   $243.50   $243.50  
  Purchase #5 $247.56   6.605%   $263.9113   $263.91   $263.90   $263.90  
  Purchase #6 $52.34   12.647%   $58.9594   $58.96   $58.95   $59.00  
  Purchase #7 $46.77   9.606%   $51.2627   $51.26   $51.25   $51.30  
  7 purchase totals = $929.35       $997.3916   $997.39   $997.40   $997.50