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 $152.90   5.102%   $160.701   $160.70   $160.70   $160.70  
  Purchase #2 $24.95   5.854%   $26.4106   $26.41   $26.40   $26.40  
  Purchase #3 $234.55   3.387%   $242.4942   $242.49   $242.50   $242.50  
  Purchase #4 $182.76   4.843%   $191.6111   $191.61   $191.60   $191.60  
  Purchase #5 $166.55   6.671%   $177.6606   $177.66   $177.65   $177.70  
  Purchase #6 $43.46   4.601%   $45.4596   $45.46   $45.45   $45.50  
  Purchase #7 $181.58   3.764%   $188.4147   $188.41   $188.40   $188.40  
  7 purchase totals = $986.75       $1,032.7518   $1,032.74   $1,032.70   $1,032.80