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 $93.35   11.106%   $103.7175   $103.72   $103.70   $103.70  
  Purchase #2 $172.63   6.710%   $184.2135   $184.21   $184.20   $184.20  
  Purchase #3 $118.49   6.839%   $126.5935   $126.59   $126.60   $126.60  
  Purchase #4 $94.79   12.341%   $106.488   $106.49   $106.50   $106.50  
  Purchase #5 $21.66   6.238%   $23.0112   $23.01   $23.00   $23.00  
  Purchase #6 $225.39   6.789%   $240.6917   $240.69   $240.70   $240.70  
  Purchase #7 $129.89   7.122%   $139.1408   $139.14   $139.15   $139.10  
  7 purchase totals = $856.20       $923.8562   $923.85   $923.85   $923.80