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 $94.70   12.418%   $106.4598   $106.46   $106.45   $106.50  
  Purchase #2 $33.32   9.861%   $36.6057   $36.61   $36.60   $36.60  
  Purchase #3 $135.85   4.815%   $142.3912   $142.39   $142.40   $142.40  
  Purchase #4 $237.87   8.492%   $258.0699   $258.07   $258.05   $258.10  
  Purchase #5 $58.46   9.143%   $63.805   $63.81   $63.80   $63.80  
  Purchase #6 $209.25   5.605%   $220.9785   $220.98   $221.00   $221.00  
  Purchase #7 $84.61   10.571%   $93.5541   $93.55   $93.55   $93.60  
  7 purchase totals = $854.06       $921.8642   $921.87   $921.85   $922.00