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 $139.44   13.289%   $157.9702   $157.97   $157.95   $158.00  
  Purchase #2 $101.41   8.140%   $109.6648   $109.66   $109.65   $109.70  
  Purchase #3 $120.80   10.238%   $133.1675   $133.17   $133.15   $133.20  
  Purchase #4 $85.31   9.615%   $93.5126   $93.51   $93.50   $93.50  
  Purchase #5 $119.98   13.270%   $135.9013   $135.90   $135.90   $135.90  
  Purchase #6 $229.88   12.649%   $258.9575   $258.96   $258.95   $259.00  
  Purchase #7 $161.68   4.514%   $168.9782   $168.98   $169.00   $169.00  
  7 purchase totals = $958.50       $1,058.1521   $1,058.15   $1,058.10   $1,058.30