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 $14.97   13.611%   $17.0076   $17.01   $17.00   $17.00  
  Purchase #2 $191.47   6.523%   $203.9596   $203.96   $203.95   $204.00  
  Purchase #3 $60.43   5.175%   $63.5573   $63.56   $63.55   $63.60  
  Purchase #4 $86.28   3.432%   $89.2411   $89.24   $89.25   $89.20  
  Purchase #5 $76.44   7.126%   $81.8871   $81.89   $81.90   $81.90  
  Purchase #6 $206.82   7.439%   $222.2053   $222.21   $222.20   $222.20  
  Purchase #7 $63.57   9.179%   $69.4051   $69.41   $69.40   $69.40  
  7 purchase totals = $699.98       $747.2631   $747.28   $747.25   $747.30