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 $57.41   4.615%   $60.0595   $60.06   $60.05   $60.10  
  Purchase #2 $209.73   10.471%   $231.6908   $231.69   $231.70   $231.70  
  Purchase #3 $9.90   13.219%   $11.2087   $11.21   $11.20   $11.20  
  Purchase #4 $241.88   6.645%   $257.9529   $257.95   $257.95   $258.00  
  Purchase #5 $35.57   13.825%   $40.4876   $40.49   $40.50   $40.50  
  Purchase #6 $186.25   6.411%   $198.1905   $198.19   $198.20   $198.20  
  Purchase #7 $212.88   8.484%   $230.9407   $230.94   $230.95   $230.90  
  7 purchase totals = $953.62       $1,030.5307   $1,030.53   $1,030.55   $1,030.60