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 $159.64   11.601%   $178.1598   $178.16   $178.15   $178.20  
  Purchase #2 $188.63   12.224%   $211.6881   $211.69   $211.70   $211.70  
  Purchase #3 $122.58   4.154%   $127.672   $127.67   $127.65   $127.70  
  Purchase #4 $246.78   3.208%   $254.6967   $254.70   $254.70   $254.70  
  Purchase #5 $247.78   10.432%   $273.6284   $273.63   $273.65   $273.60  
  Purchase #6 $188.72   6.604%   $201.1831   $201.18   $201.20   $201.20  
  Purchase #7 $228.26   7.785%   $246.03   $246.03   $246.05   $246.00  
  7 purchase totals = $1,382.39       $1,493.0581   $1,493.06   $1,493.10   $1,493.10