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 $138.45   10.396%   $152.8433   $152.84   $152.85   $152.80  
  Purchase #2 $181.31   6.242%   $192.6274   $192.63   $192.65   $192.60  
  Purchase #3 $235.46   13.849%   $268.0689   $268.07   $268.05   $268.10  
  Purchase #4 $59.65   6.586%   $63.5785   $63.58   $63.60   $63.60  
  Purchase #5 $247.50   8.318%   $268.0871   $268.09   $268.10   $268.10  
  Purchase #6 $244.74   13.327%   $277.3565   $277.36   $277.35   $277.40  
  Purchase #7 $34.74   13.473%   $39.4205   $39.42   $39.40   $39.40  
  7 purchase totals = $1,141.85       $1,261.9822   $1,261.99   $1,262.00   $1,262.00