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 $182.64   8.816%   $198.7415   $198.74   $198.75   $198.70  
  Purchase #2 $113.63   8.514%   $123.3045   $123.30   $123.30   $123.30  
  Purchase #3 $22.72   13.732%   $25.8399   $25.84   $25.85   $25.80  
  Purchase #4 $14.69   12.243%   $16.4885   $16.49   $16.50   $16.50  
  Purchase #5 $159.70   11.253%   $177.671   $177.67   $177.65   $177.70  
  Purchase #6 $140.25   13.410%   $159.0575   $159.06   $159.05   $159.10  
  Purchase #7 $230.76   9.298%   $252.2161   $252.22   $252.20   $252.20  
  7 purchase totals = $864.39       $953.3190   $953.32   $953.30   $953.30