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 $140.75   8.671%   $152.9544   $152.95   $152.95   $153.00  
  Purchase #2 $63.49   9.818%   $69.7234   $69.72   $69.70   $69.70  
  Purchase #3 $119.71   5.316%   $126.0738   $126.07   $126.05   $126.10  
  Purchase #4 $30.47   9.232%   $33.283   $33.28   $33.30   $33.30  
  Purchase #5 $201.70   13.535%   $229.0001   $229.00   $229.00   $229.00  
  Purchase #6 $167.32   9.259%   $182.8122   $182.81   $182.80   $182.80  
  Purchase #7 $216.54   4.665%   $226.6416   $226.64   $226.65   $226.60  
  7 purchase totals = $939.98       $1,020.4885   $1,020.47   $1,020.45   $1,020.50