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 $117.73   13.617%   $133.7613   $133.76   $133.75   $133.80  
  Purchase #2 $154.25   4.378%   $161.0031   $161.00   $161.00   $161.00  
  Purchase #3 $183.28   7.173%   $196.4267   $196.43   $196.45   $196.40  
  Purchase #4 $246.61   3.359%   $254.8936   $254.89   $254.90   $254.90  
  Purchase #5 $178.60   13.715%   $203.095   $203.10   $203.10   $203.10  
  Purchase #6 $250.93   12.425%   $282.1081   $282.11   $282.10   $282.10  
  Purchase #7 $75.42   10.620%   $83.4296   $83.43   $83.45   $83.40  
  7 purchase totals = $1,206.82       $1,314.7174   $1,314.72   $1,314.75   $1,314.70