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 $52.73   7.266%   $56.5614   $56.56   $56.55   $56.60  
  Purchase #2 $181.56   6.474%   $193.3142   $193.31   $193.30   $193.30  
  Purchase #3 $92.35   11.322%   $102.8059   $102.81   $102.80   $102.80  
  Purchase #4 $113.76   3.787%   $118.0681   $118.07   $118.05   $118.10  
  Purchase #5 $184.25   3.523%   $190.7411   $190.74   $190.75   $190.70  
  Purchase #6 $240.80   6.325%   $256.0306   $256.03   $256.05   $256.00  
  Purchase #7 $64.63   6.281%   $68.6894   $68.69   $68.70   $68.70  
  7 purchase totals = $930.08       $986.2107   $986.21   $986.20   $986.20